having trained with multiple Mr. Olympia competitors i can tell you they all work out around noon. not morning nor evening but mid-day.
Kai Greene was an exception - he worked out at midnight - probably to avoid waiting for machines as his workout was supersetting different muscle groups which could only work in an empty gym.
perhaps the others were also trying to avoid morning and evening rush hours - or maybe they wanted to train when they had the most energy.
personally i always lift after taking a nice shit. my bowels tell me when it’s time to train. when people ( and animals ) take a shit their energy levels go up, and conversely when you engage in a strenuous activity it makes you want to take a shit. but you probably don’t want to shit your pants while doing squats so the smart thing to do is wait until you take a nice shit and then workout immediately afterwards.
my energy also peaks in second half of the day but not before bed time as most people train.
in the gym there is a rush hour from about 4 pm to 8 pm as people get off from work or school or whatever … perhaps the pros would train later in the day except that they need to get out of the gym before the treadmill zombies start arriving …
also they have to take into consideration pre and post workout nutrition and sleep …
also keep in mind that earlier in the day your energy may be low because you’re still half asleep but if you do a good warmup and take a strong preworkout you would be able to raise this energy and then still have enough time for preworkout to clear your system so you could sleep at night …
preworkouts probably last about 5 hours or so. if you workout at 10 pm your preworkout will still be kicking at 2 AM at night … if you workout at noon it will be out of your system by the time the sun sets and you can go to sleep.
the other consideration is workout triggers protein synthesis in the muscle which must be fueled with food - if you come home from gym and go straight to sleep your muscle will eat itself ( catabolism ) as you sleep with no nutrients to replace protein breakdown following the workout. on the other hand if you finish your workout by 2 pm you can still get 2 or 3 good meals before bed to give the muscle what it needs.
of course i don’t actually go to bed with sunset so my preference is to train right before gym closing but then i stay up all night watching movies and go to sleep at sunrise.
for whatever reason the sexy lifeguard girls work the late night shift … probably because that’s when most people come so the pool management allocates the hotties for when it counts … but most people leave by 9 pm and after that i basically have the pool all to myself - it’s just me and the lifeguard chicks and it’s literally their job to watch me swim butterfly