If idle time is a problem for you, try what some of us have done. Disable VRDB generation (this only disables automatic updating every 21 days, you can still update manually any time you like), then whenever convenient just click on the "generate now" thing.
I set up a Yahoo Calendar "event" for this, recurring every 3 weeks, with an email reminder, so I don't have to remember when the next one's due. And of course that 3-week cycle is just a guideline, a few days one way or the other will make little or no difference unless you're constantly making major changes to your system.
(Edit) Oops, almost forgot ... given the nature of malware currently making the rounds, it's widely agreed that the VRDB is more or less obsolete in terms of enabling recovery, and it'll be (if they haven't changed their minds at Alwil) dropped entirely from the upcoming avast 5, currently in beta. So I haven't bothered updating my VRDB for several months now.