This subject is a can of worms with some people.
Does your amp have a standby switch?
Some people are ok using their standby switch for short stretches.
While they might full shut down if they anticipate 45 minutes or more downtime between playing sessions.
While others may not think that sensible.
I do not have a standby on my most used amp. I shut down when I walk away, always.
If I’m staying in the room, I leave it running.
At rehearsal, I turn it on, and leave it on until we’re done for the night. We usually take one “break” that could be 15 to 45 minutes long...it stays on through that every time.