There is no real means to change the interval - avast maintains a database of programs it will check for updates, typically those at higher risk of attack/exploit and or programs that have an internet facing purpose (browsers, email programs, etc. etc.).
Avast maintains this program version database, which is update along with the virus signatures. This database checks programs on your system that are on its database and check the version you have against the latest version for the program on its database.