You could try using a few attached intermediate timer events with a user task to get the notifications to go out on the schedule you want. Here's a rough idea of what it might look like:

Basically, you've got a user task that you are only using for these attached intermediate timer events. The first timer goes off a minute or so after the user task begins, and the timer's outflow path is taken and the notifications go out. The second attached timer waits until it is three days before the effective date and then interrupts the attached activity and takes the outflow path again. If you wanted something to happen after the last set of notifications, you could do that with some minor adjustments.