avast checks if there is an available connection each 40 seconds.
If there isn't, wait more 40 seconds to check. Checking does not take more than one second and, of course, does not use the Internet band.
If there is a connection, check for an update. If there is not any new file to download, wait 4 hours to start checking again. If there is an available update, start it and install it. Again, wait 4 hours to check the next time.
Some of this settings could be configurated different, I posted the default values of the avast4.ini file. The updates are incremental.
ashServ.exe sends ping packets to find out if the Internet connection is alive. You can turn this off by checking the "My computer is permanently connected to the Internet" box in the avast Program Settings > Update (Connections) page.
The program updates are released but to avoid excessive load on the servers the auto update check happens randomically every 12 hours and it's not checking every time you connect to the Internet as with the virus definitions checks. The cycle is controlled by the servers and can be changed at any time. So no later than 12 hours after the update is released, everyone should get at least one popup. The order is machine-fixed (not random-generated for each update).
Avast Free AV checks for updates every 4 hours. Avast Pro AV and IS check every 1 hour. The program already knows that the update is there, but it won't tell you until it's your turn. You have to allow the update, i.e., it's not a forced and automatic update.
The minimum intervals currently are like this:
Free AV: 120 minutes ( = 2 hours)
Pro AV, IS: 15 minutes
