From https://snapcraft.io/docs/keeping-snaps-up-to-date
Snaps update automatically, and by default, the snapd daemon checks for updates 4 times a day. Each update check is called a refresh.
You can delay updates somewhat and enable refresh app awareness ([WIP] Refresh App Awareness) to prevent updates of running applications. This won’t help in all cases because it only takes the snap itself into account, but not its dependencies.