how to reset the time avast scans
First, I’m an Avast user and not an Avast Team member.
Given you have posted in the General sub-forum what program are you using and what scan are you talking about.
My personal feeling on running manual scans differ from many others.
With a resident (on-access) scanner the need for on-demand scans is much depreciated. For the most part dormant/inert files are being scanned, the other active files are going to be scanned by the resident shields when they are activated.