When does it run?

Give a cron expression or an RRULE and a time zone, and see the rule in words and its next runs, through the nights the clocks change. Time::Keeper::Recurrence walks the rule.

Cron or RRULE

Time zone

Start, for an RRULE

Runs

*/15 9-17 * * 1-5

Read as: a cron expression, in Europe/London
Cron: 0,15,30,45 9-17 * * 1-5
RRULE: FREQ=MINUTELY;BYMINUTE=0,15,30,45;BYHOUR=9,10,11,12,13,14,15,16,17;BYDAY=MO,TU,WE,TH,FR

The next 10 runs, and more after
Run	Clock	From now
Friday, 23 October 2026, 09:00	`BST`	in 14 hours
Friday, 23 October 2026, 09:15	`BST`	in 15 hours
Friday, 23 October 2026, 09:30	`BST`	in 15 hours
Friday, 23 October 2026, 09:45	`BST`	in 15 hours
Friday, 23 October 2026, 10:00	`BST`	in 15 hours
Friday, 23 October 2026, 10:15	`BST`	in 16 hours
Friday, 23 October 2026, 10:30	`BST`	in 16 hours
Friday, 23 October 2026, 10:45	`BST`	in 16 hours
Friday, 23 October 2026, 11:00	`BST`	in 16 hours
Friday, 23 October 2026, 11:15	`BST`	in 17 hours

As iCalendar

RRULE:FREQ=MINUTELY;BYMINUTE=0,15,30,45;BYHOUR=9,10,11,12,13,14,15,16,17;BY
 DAY=MO,TU,WE,TH,FR

Try

0 9 * * 1-5 weekdays at nine
*/15 9-17 * * 1-5 every 15 minutes in working hours
FREQ=MONTHLY;BYDAY=1MO the first Monday of the month
FREQ=MONTHLY;BYMONTHDAY=-1 the last day of the month
30 2 * * * 02:30, on a night the clocks change
30 1 * * * 01:30, through the hour that comes twice