It’s difficult to really know for sure because I’ve not listened to the same music at 30 minutes, 1 hour, 2 hours etc. It’s also difficult to remember & accurately compare w/ that time lapse in between. I don’t think our sonic memory is that good over time, even relatively short amounts.
“Warm up” time could also be be within in our brains & it takes me time to relax, unwind & really get into the music & really enjoy it.
That all said, I have noticed w my Rogers EFH 200 Mark II ( 2- KT 150’s per side & a seriously large power transformer) that the sound definitely sounds more full body & fleshed out after about 1 hour. Beyond that , I can’t say much.