You don't need any additional code to support reminder notifications. The changes can me made when you create the notificaiton objects.
I have made a change that allows you to pass in the notification date/time and then the notificaiton will go out at that time only. I had to make one change to a query to support this.
As soon as I finish testing this can go into OpenACS and I can release a new notiifcations version.