It is possible to run On-Demand backups during the maintenance window. You can even run scheduled backups then, but it's obviously not recommended.

In the user guide it states:

"The maintenance window is that portion of each day reserved to perform routine server maintenance activities, primarily checkpoint creation and validation.There might be brief periods of time when backup or administrative activities are not allowed. Although backups can be initiated during the maintenance window, doing so impacts both the backup and maintenance activities. For this reason, minimize any backup or administrative activities during the maintenance window. You can, however, perform restores.

...

You might want to advise users to avoid initiating any on-demand backups from their client computers during the first hour and thirty minutes of the maintenance window"

If you want to stop client-initiated backups, you can go to the Policy section in Avamar Administrator, edit the clients and remove the check-mark for "Allow client initiated backups" if you want. (Disclaimer: test this first, as I have not tried it). I don't know if there is a global setting for this.

Regards,

Steve

I'm actually trying to prevent my users from doing on-demand backups during the window. I have yet to find out how to enable something like this

Yes, that is the key to my initial question.  Customers have asked for a means of preventing on-demand backups during maintenance.  This doesn't mean on-demand backups should never be allowed.  Only that they need to be prevented from initiating at key times to reduce interfering with critical maintenance activities.

If anyone has insight into this question - please jump in.

Suspending the dispatchers using "avmaint suspend" is the only practical way I can think of to prevent on-demand backups during maintenance. The problem with this approach is that it would prevent all backup and restore activity.