How to disable or set Snapshots

The snapshot feature in P8 is nice, but the time is inappropriate - snapshots are created automatically during the highest traffic on the installed Windows 2003 server and stops everthing in our office.

How can we disable the snapshot feature or at least set the time to midnight or so? The popup menus in the settings are greyed out, regardless if the VM is running or not.

I've found a setting, but I cannot set a time of the day, only a rhythm of reccurring hours.