Maintenance for the week of March 25:
• [COMPLETE] ESO Store and Account System for maintenance – March 28, 9:00AM EDT (13:00 UTC) - 12:00PM EDT (16:00 UTC)
On the day of the month that the sub is purchased or renewed.
Edit: to be more clear, all of the crowns for the entire sub duration are sent at the same time, they are not sent monthly unless the subscription is renewed monthly.