I had a friend who had a gig playing for a touring band that was pretty big and impressive in the 1970’s, but had dropped in significance by the 1990’s. Being on the tour bus with the band was among the coolest thing I have ever done. After the Southern Spirits Tour where I first learned I was only a few degrees from fame, they came through town several times and it was always a blast.
The guys in the band loved to go out to bars and clubs that had live music and sort of take over the bandstand. After the first few times when I would get a call once they in town, I would know they were coming and a couple of the guys might come water skiing with us at Canyon Lake during the day - before the show that night. I would usually ride on the bus with them to the venue and then sit backstage while they were on.
If they did leave that night, it was right after the show. If they were not the closing act they would sometimes be rolling to the next gig before the last band was done on stage. (They usually were the headliner, but if not they were on right before the headliner- they were too big to ever be the opening act. They did do a lot of those rock gods of the seventies type shows however. The best was when they did a corporate gig-- no other bands, arrive just before going on, then an hour of signing headshots and right back on the bus and back to the hotel in time to hit the bars.)
When they took off right after the show, they always asked if I wanted to stay on the bus and go to the show in Tucson or LA but I never did that. If they were not leaving that night they would want to go play some more. They did seem to get a high from performing. The best night was at Chars Has The Blues where the drummer and my buddy on keys played with the rest of the locals and closed with a thirty minute version of Brick House– totally rocked the house off the foundations. Another night at The Rhythm Room on Indian School was also a good time. My favorites were the couple of times we went to David D’s Melody Lounge. They didn’t have music every night – but nights that they did were pretty great and the guys liked playing with those musicians, thought very highly of them.
My impression based upon that limited experience was that the days just dragged until it was finally time to gig and then they were finally ALIVE!
I was told from a former roadie (who did not share my view that these were all Southern Gentlemen of great refinement), and my friend the piano player (who was a gentleman from the South of very high refinement) that the schedule was really determined by the crew. They had to set up all day including a sound check, then wait for the show to be over (sometimes waiting for another band to play after our guys were off stage) then strike the entire show, put it into rolling boxes and load it into one or two trucks, strap everything down and sleep on this weird half truck, half bus full of bunk-bed style sleeping births while they drove to the next show. Then they would often set up the next show with local help and only then get to a hotel where they had to double up (the “talent” each got their own rooms). Getting a workout in on any kind of steady schedule was a challenge they always had while on the road.
As a direct answer to the OP, I recall reading that John Lennon and Harry Nilsson would often attend the shows of other performers if they had the night off (and often drew more attention than may have been prudent). In a like manner, The Rat Pack were quite famous for doing the same in Las Vegas. According to many sources, most performers loved having such high profile attenders-- others HATED them for it. Sometimes Martin, Sinatra, and Davis Jr. would get up on stage and crack jokes and sing snippets of songs – which they considered a gift to the artist. The artists didn’t always agree with the high opinion they had of themselves.