An option is to have a report of Notifications to be sent daily, and have a user receive this internal report daily. Then make a URL formula button to "toggle" a checkbox field, triggering a Notification, and also record the date the checkbox was toggled so as to be able to refresh the screen with one less record. Then the user clicks the next record on the report. It also possible to have a little pop up as feedback to the user that their click "took" and then they can just click click lock down the report to fire off the emails to the outside users.
The form which goes out could have an embedded "report" on it - for example, each record might be a (non-User) client having an embedded report of their open orders.
Once that was working, then it would be possible to write a script to walk down that report to trigger the Open email Notifications.
