Even though this thread is 3 years old I'd like to comment as reference for others to find later on.
I'm doing the same, turn both radios off when the rest of the conference building is off. This is preferred over turning PoE off; AP is still reachable and faster to turn on again.
enable config ap 58:fb:96:xx:yy:zz no radio 2.4 wlan-service no radio 5 wlan-service end end disable
Do not forget to send an "end" after the radio commands, this works as commit/save. And be patient! 5GHz needed some 25sec to disappear whereas 2.4GHz was active for 80sec after the commit. I checked the spectrum utilisation with a Wi-Spy.
So yes, the commands do work. They just need some time to think about your input...
This was with an Unleashed R510 on 200.8.a.b.c.d in July 2021