Welcome and indeed 2 minutes is enough to warm up the tubes...I give them 10 -15 minutes as stated ........Ill just keep doing what has worked for me but thought id offer my opinion.

Just looked at my manual for the vintage/modern marshall and it states to turn on without standby on and after two minutes warmup you are good to go then you can hit standby if not playing.: Exactly opposite of my fender hrd manual:

Also I have seen personally the HT fuse,main fuse and tubes go bad when somone has turned on their tube amp with the stanby switch on and within a minute or two flip the switch to play just to hear a pop..of course there is a delay for a few seconds while the HT or Main fuse does the slow burn


Anyways to each his own