From this post it sounds like all day events on Google Calendar are set to remind at 5pm the day before. Is there any way to change that value? It doesn't look like it accepts a negative value for the reminder. I'd like the reminder around 8pm or 9pm in many cases. For example, I have an all day event to remind me which days are "trash days" and I'd like the reminder at 9pm the night before, after the kids go to sleep, so that I remember to put the trash can out. Is there a setting somewhere or am I forced to make these 12am events instead?
I'm not sure if they changed that or if it is a setting somewhere, but every time I setup an all day event, the reminder pops up the set time before midnight. So, if I have event E, an all day event for the date of 29 Aug 2013 and I set a reminder for 5 hours before the event starts, then the reminder will execute on the day of 28 Aug 2013 at 19:00 / 7 pm.
So in your case it should be set for 3 hours before event starts. Best way to figure this out is to test it. Every time I've done this it was calculate from midnight.