I am very occasionally late to rehearsal. I don’t love it, but I do like to learn one important thing about the ensemble.
The ensemble that is owned by the conductor waits for the conductor to start. The ensemble that is self-owned starts when it’s time to start.
I love walking into the room and hearing a group already singing, or checking the sound system. I don’t want to be the boss of the group, just its facilitator, and I know that that’s what’s happening when I walk in late and the ensemble hasn’t waited for me.
I don’t love walking in late, but hearing an ensemble rehearsing without me is a pretty nice silver lining.