@ roro
I have no problem and I'm on dial-up too.
Because dial-up differs from broadband, in that every time you re-connect avast would check for updates. Now if you are only going on-line to do something quick, collect email, etc. you might want to be able to do this and get off-line without a check taking place.
So I too delay my update check by 10 minutes, which allows for a quick jump on-line and off again without the update check being carried out. This suits me very well and may do so for your friend.
You need to edit (using notepad) the [InetWD] section of the C:\Program Files\Alwil Software\Avast4\Data\avast4.ini file and add the following line (depending on your connection type enter one or other of the Bold lines below):
Dial-up connections, add this line:
RASWaitSeconds=600 and UseRAS=1 if not present (or edit UseRAS=0 to UseRAS=1)
[InetWD]
UseRAS=1
RASWaitSeconds=600
When complete save the changes, avast's self-defence module will ask for confirmation, etc. answer Yes.
The figure is seconds and the above equates to ten minutes, you could try that and adjust lower if required, 300, 240, etc.