pj,
The interval for the VRDB is not short by default. It is set for 3 weeks. Before we go further, what version do you have?
Version 4.1 has just been released, and your Avast should have notified you of that.
If it has not, do a manual program update. Version 4.1 will allow a manual start of the VRDB form the I ball. You no longer have to modify the Avast4.ini file.
Update your program first, then manually run the VR :DDB and check the date once more.
Let me know what happens.