Upgrading from Linux mint 20 to 21-how to know when to take a snapshot?

Newbie questions: the upgrade instructions say be up to date and to prepare several snapshots during the upgrade process. How do I know when to snapshot? I got to the point of the time shift window opening for the first time and the checking snapshots circle of happy death kept going round and round. Am I supposed to create a snapshot manually and if so, is there an instruction that tells me to do so?