fix(Schedule Node): Fix hourly intervals that don't divide evenly into 24h (#29778)

packages/nodes-base/nodes/Schedule/GenericFunctions.ts

@@ -115,7 +115,14 @@ export const toCronExpression = (interval: ScheduleInterval, nodeKey: string): C
 	if (interval.field === 'minutes') return `${second} */${interval.minutesInterval} * * * *`;
 
 	const minute = interval.triggerAtMinute ?? stableInt(nodeKey, 'minute', 0, 60);
-	if (interval.field === 'hours') return `${second} ${minute} */${interval.hoursInterval} * * *`;
+	if (interval.field === 'hours') {
+		const hours = interval.hoursInterval;
+		if (24 % hours === 0) return `${second} ${minute} */${hours} * * *`;
+		// `*/${hours}` fires only at clock hours divisible by ${hours}: for 18 h
+		// that is 00:xx and 18:xx — an 18 h gap then a 6 h gap, not a steady
+		// 18 h rhythm. Fire every hour; recurrenceCheck enforces elapsed time.
+		return `${second} ${minute} * * * *`;
+	}
 
 	// Since Cron does not support `*/` for days or weeks, all following expressions trigger more often, but are then filtered by `recurrenceCheck`
 	const hour = interval.triggerAtHour ?? stableInt(nodeKey, 'hour', 0, 24);

packages/nodes-base/nodes/Schedule/test/GenericFunctions.test.ts

@@ -94,6 +94,15 @@ describe('toCronExpression', () => {
 			TEST_SEED,
 		);
 		expect(result1).toEqual('56 19 */3 * * *');
+
+		const result2 = toCronExpression(
+			{
+				field: 'hours',
+				hoursInterval: 18,
+			},
+			TEST_SEED,
+		);
+		expect(result2).toEqual('56 19 * * * *');
 	});
 
 	it('should return cron expression for days interval', () => {

packages/nodes-base/nodes/Schedule/test/ScheduleTrigger.node.test.ts

@@ -61,6 +61,54 @@ describe('ScheduleTrigger', () => {
 			expect(emit).toHaveBeenCalledTimes(2);
 		});
 
+		it('should emit repeatedly for hourly intervals that do not divide evenly into a day', async () => {
+			const { emit } = await testTriggerNode(ScheduleTrigger, {
+				timezone,
+				node: { parameters: { rule: { interval: [{ field: 'hours', hoursInterval: 18 }] } } },
+				workflowStaticData: { recurrenceRules: [] },
+			});
+
+			expect(emit).not.toHaveBeenCalled();
+
+			jest.advanceTimersByTime(HOUR);
+			expect(emit).toHaveBeenCalledTimes(1);
+
+			jest.advanceTimersByTime(17 * HOUR);
+			expect(emit).toHaveBeenCalledTimes(1);
+
+			jest.advanceTimersByTime(HOUR);
+			expect(emit).toHaveBeenCalledTimes(2);
+
+			jest.advanceTimersByTime(17 * HOUR);
+			expect(emit).toHaveBeenCalledTimes(2);
+
+			jest.advanceTimersByTime(HOUR);
+			expect(emit).toHaveBeenCalledTimes(3);
+		});
+
+		it('should emit every 18 hours when triggerAtMinute is explicitly set to 0', async () => {
+			const { emit } = await testTriggerNode(ScheduleTrigger, {
+				timezone,
+				node: {
+					parameters: {
+						rule: { interval: [{ field: 'hours', hoursInterval: 18, triggerAtMinute: 0 }] },
+					},
+				},
+				workflowStaticData: { recurrenceRules: [] },
+			});
+
+			expect(emit).not.toHaveBeenCalled();
+
+			jest.advanceTimersByTime(HOUR);
+			expect(emit).toHaveBeenCalledTimes(1);
+
+			jest.advanceTimersByTime(17 * HOUR);
+			expect(emit).toHaveBeenCalledTimes(1);
+
+			jest.advanceTimersByTime(HOUR);
+			expect(emit).toHaveBeenCalledTimes(2);
+		});
+
 		it('should emit on schedule defined as a cron expression', async () => {
 			const { emit } = await testTriggerNode(ScheduleTrigger, {
 				timezone,