Depends a lot of your system (how many executable files do you have) and what is running in background. Like David said, maybe something between 5 minutes and one hour :-\
I suppose too, but you can see the date after some days and check if the VRDB is working…
I think not. Maybe I’m wrong but avast! must detect the state of a ‘screen saver running’ to start VRDB… :-\