Hi bro, in my almost ten years of iMac usage, I even used it 2 to 3 days nonstop without turning it OFF. so far, no problem has happened. Mac mini users also use it the same way. Proper power surge protection where the iMac power supply is connected is very well sufficient. Make sure your building has an appropriate connection to earth too.
Then there is no requirement to shut it down at certain times, but if you notice any hangs or hiccups, you may turn off the mac once and continue working on it. There shouldn’t be a problem.