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

FREQ=MONTHLY;BYDAY=1MO

Read as: an RRULE, in Europe/London
RRULE: FREQ=MONTHLY;BYDAY=1MO

The next 10 runs, and more after
Run	Clock	From now
Monday, 2 November 2026, 10:00	`GMT`	in 11 days
Monday, 7 December 2026, 10:00	`GMT`	in 46 days
Monday, 4 January 2027, 10:00	`GMT`	in 74 days
Monday, 1 February 2027, 10:00	`GMT`	in 102 days
Monday, 1 March 2027, 10:00	`GMT`	in 130 days
Monday, 5 April 2027, 10:00	`BST`	in 165 days
Monday, 3 May 2027, 10:00	`BST`	in 193 days
Monday, 7 June 2027, 10:00	`BST`	in 228 days
Monday, 5 July 2027, 10:00	`BST`	in 256 days
Monday, 2 August 2027, 10:00	`BST`	in 284 days

The clocks change

Sunday, 25 October 2026. The clocks go back an hour at 02:00, to 01:00 (GMT). The times from 01:00 to 01:59 happen twice.

A run this rule makes in them comes once, at the first.

Sunday, 28 March 2027. The clocks go forward an hour at 01:00, to 02:00 (BST). The times from 01:00 to 01:59 do not happen that night.

A run this rule would make in them comes as much later as the clocks moved.

As iCalendar

DTSTART;TZID=Europe/London:20260105T100000
RRULE:FREQ=MONTHLY;BYDAY=1MO

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