Now (126.96.36.199) it is not possible to set a reminder for events in the birthday calendar.
I understand the reminder for a birthday and that the birthday is a day event. It is however a bit silly to have a reminder set for the birthday that goes off at 2300 at night. Like that is helpful when I sleep.
Please allow me to modify the reminders for birthdays.
Yes, of course, it would be good to be able to set the reminder time e.g. in Slovakia we use name days, I also have an all-day event created for it (similar to birthdays), my reminder is set to 12 or 6 hours.