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;BYMONTHDAY=-1

Read as: an RRULE, in UTC
RRULE: FREQ=MONTHLY;BYMONTHDAY=-1

The next 10 runs, and more after
Run	Clock	From now
Saturday, 31 October 2026, 18:00	`UTC`	in 9 days
Monday, 30 November 2026, 18:00	`UTC`	in 39 days
Thursday, 31 December 2026, 18:00	`UTC`	in 70 days
Sunday, 31 January 2027, 18:00	`UTC`	in 101 days
Sunday, 28 February 2027, 18:00	`UTC`	in 129 days
Wednesday, 31 March 2027, 18:00	`UTC`	in 160 days
Friday, 30 April 2027, 18:00	`UTC`	in 190 days
Monday, 31 May 2027, 18:00	`UTC`	in 221 days
Wednesday, 30 June 2027, 18:00	`UTC`	in 251 days
Saturday, 31 July 2027, 18:00	`UTC`	in 282 days

As iCalendar

DTSTART:20260131T180000Z
RRULE:FREQ=MONTHLY;BYMONTHDAY=-1

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