diff --git a/js/planner.js b/js/planner.js
index 276cfa5..a759132 100644
--- a/js/planner.js
+++ b/js/planner.js
@@ -2133,58 +2133,141 @@ function initTimeline(planId) {
     let timelinePan = null;
     let suppressNextTimelineClick = false;
     let timelineDrag = null;
+    let dragPreviewEl = null;
+    let dragPreviewRow = null;
+    let dragPreviewTrack = null;
+    let pendingDragPreview = null;
+    let dragPreviewFrame = 0;
 
     function removeDragPreview() {
-        document.getElementById('timeline-drag-preview')?.remove();
-        timeline.querySelectorAll('.timeline-player-row--drop-ok, .timeline-player-row--drop-bad')
-            .forEach(row => row.classList.remove('timeline-player-row--drop-ok', 'timeline-player-row--drop-bad'));
+        if (dragPreviewFrame) cancelAnimationFrame(dragPreviewFrame);
+        dragPreviewFrame = 0;
+        pendingDragPreview = null;
+        dragPreviewEl?.remove();
+        dragPreviewEl = null;
+        dragPreviewTrack = null;
+        dragPreviewRow?.classList.remove('timeline-player-row--drop-ok', 'timeline-player-row--drop-bad');
+        dragPreviewRow = null;
     }
 
-    function updateDragPreview(event) {
-        if (!timelineDrag) return;
-        removeDragPreview();
+    function setDragPreviewRow(row, valid) {
+        if (dragPreviewRow && dragPreviewRow !== row) {
+            dragPreviewRow.classList.remove('timeline-player-row--drop-ok', 'timeline-player-row--drop-bad');
+        }
+        dragPreviewRow = row;
+        row.classList.toggle('timeline-player-row--drop-ok', valid);
+        row.classList.toggle('timeline-player-row--drop-bad', !valid);
+    }
 
-        const track = event.target.closest('.timeline-player-row .timeline-track');
-        const row = event.target.closest('.timeline-player-row');
+    function ensureDragPreview(track) {
+        if (!dragPreviewEl) {
+            dragPreviewEl = document.createElement('div');
+            dragPreviewEl.id = 'timeline-drag-preview';
+            dragPreviewEl.innerHTML = `
+                <span class="timeline-drag-preview-active"></span>
+                ${timelineDrag.icon ? `<img src="${escHtml(timelineDrag.icon)}" alt="">` : ''}
+                <span>${escHtml(timelineDrag.label)}</span>
+            `;
+        }
+        if (dragPreviewTrack !== track) {
+            track.appendChild(dragPreviewEl);
+            dragPreviewTrack = track;
+        }
+        return dragPreviewEl;
+    }
+
+    function updateDragPreview(target, clientX) {
+        if (!timelineDrag) return;
+
+        const track = target.closest('.timeline-player-row .timeline-track');
+        const row = target.closest('.timeline-player-row');
         if (!track || !row) return;
 
-        const plan = getPlan(planId);
+        const plan = timelineDrag.plan ?? getPlan(planId);
         if (!plan) return;
-        const rect = track.getBoundingClientRect();
-        const duration = planDurationMs(plan);
-        const deltaPx = event.clientX - timelineDrag.startClientX;
+        const rect = timelineDrag.track === track && timelineDrag.trackRect
+            ? timelineDrag.trackRect
+            : track.getBoundingClientRect();
+        timelineDrag.track = track;
+        timelineDrag.trackRect = rect;
+        const duration = timelineDrag.planDuration || planDurationMs(plan);
+        const deltaPx = clientX - timelineDrag.startClientX;
         const timestamp = Math.max(0, timelineDrag.startTimestamp + (deltaPx / rect.width) * duration);
         const left = Math.max(0, Math.min(100, (timestamp / duration) * 100));
         const durationPct = Math.max(1.2, Math.min(100 - left, (timelineDrag.durationSec * 1000 / duration) * 100));
         const cooldownPct = Math.max(durationPct, Math.min(100 - left, (timelineDrag.cooldownSec * 1000 / duration) * 100));
         const activePct = Math.min(100, (durationPct / cooldownPct) * 100);
+        const rowJob = row.dataset.job;
         const valid = row.dataset.ability === timelineDrag.ability
-            && jobCanUseAbility(row.dataset.job, timelineDrag.ability)
-            && !assignmentOverlapsJob(plan, row.dataset.job, timelineDrag.ability, timestamp, {
-                mechanicId: timelineDrag.mechanicId,
-                ability: timelineDrag.ability,
-                job: timelineDrag.job,
-            }, {
-                ability: timelineDrag.ability,
-                job: row.dataset.job,
-                durationSeconds: timelineDrag.durationSec,
-                cooldownSeconds: timelineDrag.cooldownSec,
-            });
+            && jobCanUseAbility(rowJob, timelineDrag.ability)
+            && !dragTimestampOverlapsJob(rowJob, timestamp);
 
-        row.classList.add(valid ? 'timeline-player-row--drop-ok' : 'timeline-player-row--drop-bad');
+        setDragPreviewRow(row, valid);
 
-        const preview = document.createElement('div');
-        preview.id = 'timeline-drag-preview';
+        const preview = ensureDragPreview(track);
         preview.className = `timeline-drag-preview ${valid ? '' : 'timeline-drag-preview--bad'}`;
         preview.style.left = `${left}%`;
         preview.style.setProperty('--cd-width', `${cooldownPct}%`);
         preview.style.setProperty('--active-width', `${activePct}%`);
-        preview.innerHTML = `
-            <span class="timeline-drag-preview-active"></span>
-            ${timelineDrag.icon ? `<img src="${escHtml(timelineDrag.icon)}" alt="">` : ''}
-            <span>${escHtml(timelineDrag.label)}</span>
-        `;
-        track.appendChild(preview);
+    }
+
+    function scheduleDragPreview(event) {
+        pendingDragPreview = {
+            target: event.target,
+            clientX: event.clientX,
+        };
+        if (dragPreviewFrame) return;
+        dragPreviewFrame = requestAnimationFrame(() => {
+            dragPreviewFrame = 0;
+            const next = pendingDragPreview;
+            pendingDragPreview = null;
+            if (next) updateDragPreview(next.target, next.clientX);
+        });
+    }
+
+    function buildDragOverlapEntries(plan, ref) {
+        const ignoredActivation = assignmentEntryForRef(plan, ref);
+        const byJob = new Map();
+        const addEntry = (job, entry) => {
+            if (!byJob.has(job)) byJob.set(job, []);
+            byJob.get(job).push(entry);
+        };
+
+        for (const mechanic of visiblePlanMechanics(plan)) {
+            for (const assignment of mechanic.assignments ?? []) {
+                if (assignment.ability !== ref.ability) continue;
+                if (sameAssignmentRef(mechanic, assignment, ref)) continue;
+
+                const start = assignmentStartMs(mechanic, assignment);
+                const entry = {
+                    start,
+                    end: start + assignmentWindowMs(assignment),
+                };
+                if (ignoredActivation) {
+                    const fullEntry = { mechanic, assignment, ...entry };
+                    if (assignmentsOverlapActiveFrame(plan, ignoredActivation, fullEntry)) continue;
+                }
+
+                const assignedJob = assignment.job ?? '';
+                if (assignedJob) {
+                    addEntry(assignedJob, entry);
+                } else {
+                    (plan.jobComposition ?? [])
+                        .filter(job => jobCanUseAbility(job, assignment.ability))
+                        .forEach(job => addEntry(job, entry));
+                }
+            }
+        }
+
+        return byJob;
+    }
+
+    function dragTimestampOverlapsJob(rowJob, timestamp) {
+        if (!timelineDrag) return false;
+        const candidateStart = Math.max(0, timestamp);
+        const candidateEnd = candidateStart + timelineDrag.windowMs;
+        const entries = timelineDrag.overlapEntriesByJob?.get(rowJob) ?? [];
+        return entries.some(entry => candidateStart < entry.end && candidateEnd > entry.start);
     }
 
     timeline.addEventListener('pointerdown', e => {
@@ -2386,6 +2469,8 @@ function initTimeline(planId) {
         transparent.height = 1;
         e.dataTransfer.setDragImage(transparent, 0, 0);
         timelineDrag = {
+            plan,
+            planDuration: planDurationMs(plan),
             mechanicId: block.dataset.mechanicId,
             ability: block.dataset.ability,
             job: block.dataset.job,
@@ -2395,6 +2480,14 @@ function initTimeline(planId) {
             startTimestamp: assignmentStartMs(found.mechanic, found.assignment),
             durationSec: assignmentDurationSeconds(found.assignment),
             cooldownSec: assignmentCooldownSeconds(found.assignment),
+            windowMs: assignmentWindowMs(found.assignment),
+            overlapEntriesByJob: buildDragOverlapEntries(plan, {
+                mechanicId: block.dataset.mechanicId,
+                ability: block.dataset.ability,
+                job: block.dataset.job,
+            }),
+            track: null,
+            trackRect: null,
         };
         e.dataTransfer.effectAllowed = 'move';
         e.dataTransfer.setData('text/plain', JSON.stringify({
@@ -2409,7 +2502,7 @@ function initTimeline(planId) {
     timeline.addEventListener('dragover', e => {
         if (e.target.closest('.timeline-player-row .timeline-track')) {
             e.preventDefault();
-            updateDragPreview(e);
+            scheduleDragPreview(e);
         }
     });
 
@@ -2418,6 +2511,9 @@ function initTimeline(planId) {
     });
 
     timeline.addEventListener('drop', e => {
+        if (dragPreviewFrame) cancelAnimationFrame(dragPreviewFrame);
+        dragPreviewFrame = 0;
+        pendingDragPreview = null;
         removeDragPreview();
         const track = e.target.closest('.timeline-player-row .timeline-track');
         const row = e.target.closest('.timeline-player-row');