Set your server time (System - Global Configuration - Server) to something different from UTC. Testing this is more intuitive, if your server is actually located in this time zone (e.g. CEST = UTC+2). Otherwise, you'd have to do the appropriate calculations in order to check if the time fits.
Check the time zone setting of your own user (top right: User Menu - Edit Account - Basic Settings) to match your actual time zone (or to compensate for the "wrong" server time zone from step 1 if your server is on UTC).
At Components - Tags, create a new tag and save it.
Edit the tag and look at the created and modified date.