Bought an NAD 3020. Question for the experts here!

34dean,

If I recall correctly, the amp you bought was just fully refurbished, correct? Because it was just redone, I wouldn't leave it on when if I we're not around to keep an eye on it, at least for a few weeks. After that, if you're certain it is in good/safe operating condition, I would leave it on days when you think you'll be listening to it and turn it off when you are going to be away for day/days at a time.

Not sure there is any correct answer. You might want to do a little experimenting and see how it sounds cold/warm/hot and make a sound quality decision. If there is no obvious sound quality difference, turn it off when not in use.

Enjoy your new (old) amp.......

If it is the original edition then that is an old amp!  I own the 3040 of the same vintage and use it in my garage to power outdoor speakers.  Mine has never needed repair in the 35 years I have owned it and it survives 90+ degree heat in the summer and freezing temperatures in the winter.  I try and turn it on/off when using/not using it but sometimes leave it on for a couple of days unintentionally.

I can provide two observations, first, my amp has handled many, many on/off cycles without fail and, second, a 35-year old amp can fail at any time.  One last thing, because it does get slightly warm and because it is so old, I would probably opt for turning on/off. 

Sorry, I should have mentioned that the amp was just completely restored, recapped and serviced.  
I would like it to last a long time so I certainly do not want to harm it by leaving it on all of the time.  Perhaps I should just turn it on an hour or so before I know I will be listening and then turn off each time?