diff --git a/apps/web/src/components/timeline/timelineHover.test.ts b/apps/web/src/components/timeline/timelineHover.test.ts
new file mode 100644
index 0000000..7bb7896
--- /dev/null
+++ b/apps/web/src/components/timeline/timelineHover.test.ts
@@ -0,0 +1,102 @@
+import { describe, expect, it, vi } from "vitest";
+import {
+  buildDemandHoverData,
+  findVacationHit,
+  scheduleVacationHoverUpdate,
+} from "./timelineHover.js";
+
+describe("timelineHover", () => {
+  it("matches vacation hits inclusively across differing time components", () => {
+    const hit = findVacationHit(
+      [
+        {
+          id: "vacation_1",
+          startDate: "2026-04-10T15:00:00.000Z",
+          endDate: "2026-04-12T01:00:00.000Z",
+        },
+      ],
+      new Date("2026-04-12T23:59:59.000Z"),
+    );
+
+    expect(hit?.id).toBe("vacation_1");
+  });
+
+  it("does not schedule a second hover frame while one is already pending", () => {
+    const frameRef = { current: 42 };
+    const hoveredKeyRef = { current: null };
+    const onHoverChange = vi.fn();
+    const requestAnimationFrameMock = vi.fn();
+
+    vi.stubGlobal("requestAnimationFrame", requestAnimationFrameMock);
+
+    scheduleVacationHoverUpdate({
+      frameRef,
+      hoveredKeyRef,
+      resourceId: "resource_1",
+      clientX: 160,
+      rect: {} as DOMRect,
+      xToDate: () => new Date("2026-04-10T00:00:00.000Z"),
+      vacations: [{ id: "vacation_1", startDate: "2026-04-10", endDate: "2026-04-12" }],
+      onHoverChange,
+    });
+
+    expect(requestAnimationFrameMock).not.toHaveBeenCalled();
+    expect(onHoverChange).not.toHaveBeenCalled();
+  });
+
+  it("suppresses duplicate hover notifications when the hovered vacation does not change", () => {
+    const scheduledFrames: Array<(timestamp: number) => void> = [];
+
+    vi.stubGlobal("requestAnimationFrame", vi.fn((callback: (timestamp: number) => void) => {
+      scheduledFrames.push(callback);
+      return 7;
+    }));
+
+    const frameRef = { current: null as number | null };
+    const hoveredKeyRef = { current: "resource_1:vacation_1" };
+    const onHoverChange = vi.fn();
+
+    scheduleVacationHoverUpdate({
+      frameRef,
+      hoveredKeyRef,
+      resourceId: "resource_1",
+      clientX: 160,
+      rect: {} as DOMRect,
+      xToDate: () => new Date("2026-04-11T12:00:00.000Z"),
+      vacations: [{ id: "vacation_1", startDate: "2026-04-10", endDate: "2026-04-12" }],
+      onHoverChange,
+    });
+
+    expect(frameRef.current).toBe(7);
+    expect(scheduledFrames).toHaveLength(1);
+    scheduledFrames[0]!(0);
+
+    expect(frameRef.current).toBeNull();
+    expect(onHoverChange).not.toHaveBeenCalled();
+    expect(hoveredKeyRef.current).toBe("resource_1:vacation_1");
+  });
+
+  it("omits cost data and clamps total hours to at least one day for inverted demand ranges", () => {
+    const hoverData = buildDemandHoverData({
+      roleEntity: null,
+      role: null,
+      project: {
+        name: "Project Atlas",
+        shortCode: "ATL",
+      },
+      requestedHeadcount: 2,
+      unfilledHeadcount: 1,
+      startDate: "2026-04-14",
+      endDate: "2026-04-13",
+      hoursPerDay: 6,
+      percentage: 50,
+      status: "open",
+      dailyCostCents: 0,
+    } as never);
+
+    expect(hoverData.roleName).toBe("Open demand");
+    expect(hoverData.totalHours).toBe(6);
+    expect(hoverData).not.toHaveProperty("dailyCostCents");
+    expect(hoverData).not.toHaveProperty("totalCostCents");
+  });
+});
diff --git a/apps/web/src/components/timeline/timelineHover.ts b/apps/web/src/components/timeline/timelineHover.ts
index 4868da3..b85c51a 100644
--- a/apps/web/src/components/timeline/timelineHover.ts
+++ b/apps/web/src/components/timeline/timelineHover.ts
@@ -7,6 +7,11 @@ export type TooltipPosition = {
   top: number;
 };
 
+function toUtcDayTimestamp(value: Date | string): number {
+  const date = new Date(value);
+  return Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate());
+}
+
 export function updateTooltipPosition(
   positionRef: MutableRefObject<TooltipPosition>,
   tooltipRef: RefObject<HTMLDivElement | null>,
@@ -32,17 +37,13 @@ export function findVacationHit<T extends { startDate: Date | string; endDate: D
   vacations: T[],
   date: Date,
 ): T | null {
-  const time = new Date(date);
-  time.setHours(0, 0, 0, 0);
-  const target = time.getTime();
+  const target = toUtcDayTimestamp(date);
 
   return (
     vacations.find((vacation) => {
-      const start = new Date(vacation.startDate);
-      start.setHours(0, 0, 0, 0);
-      const end = new Date(vacation.endDate);
-      end.setHours(0, 0, 0, 0);
-      return target >= start.getTime() && target <= end.getTime();
+      const start = toUtcDayTimestamp(vacation.startDate);
+      const end = toUtcDayTimestamp(vacation.endDate);
+      return target >= start && target <= end;
     }) ?? null
   );
 }