Do you want to simply send an email every day at 8h15am ? Do you mind if the Event Frame is of zero duration? Will there be any data on the Event Frame? Which version of AF/Analytics/Notifications are you running?
If you don't really mind what's on the Event Frame or it's duration, you can simply have the same EndTrigger as the StartTrigger and schedule the analysis to be periodic. The analysis service will create an Event Frame and immediately close it resulting in a 0 duration Event Frame. The Notifications Service will pick it up and send the Notification.
Hope this helps,
I have a suggestion for you:
You could create a performance equation running on the PI Server that records a value of 1 or 0 every interval you define or at certain times such as
If (time of day = 08:15 AM) Then
Else If (time of day > 10:25 AM AND time of day < 10:35 AM) Then
do something else
where the "do something" is the event frame start condition and and the "do something else" is the event frame end condition. From there you can set up the attributes that follow the value of that performance equation and configure your pi notification rule.