Google-calendar – Does a Google Calendar Reminder that’s marked as all day give out notification

Now you can set when you will be notified for All-day events in the Google Calendar Settings.

1. Go to calendar.google.com in your browser
2. Click on the gear icon in the upper right and choose Settings
3. Choose Calendars from the top menu
4. Select 'Edit notifications' for the calendar you wish to edit this setting for. The first calendar listed will be your primary calendar, and usually the one you'll want to work with
5. The second setting All-day event notifications allows you to how many days before and at what time you wish to receive the notification
6. Be sure to click Save before leaving this page

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.