You don't say which updates you are talking about ?
Given your other topic -
https://forum.avast.com/index.php?topic=314298.0 - I can only assume you are talking about the Program update as only they require a restart.
There is no setting a specific time or how often, it is either Automatic or Manual.
You can change this in the settings, I have mine set to manual (see attached image) mainly because I'm on the forums a lot, so I see what is going on in the beta testing and what is coming in the new update. Setting it to manual if you aren't on top of what is going on in the program update developments could leave you well behind and out of date.
