No. AM stations are allowed to test in any way they want after midnight. Some examples are testing a single tower emergency set-up for DA stations, testing day power or antenna, tuning night system, doing a Proof of Performance test, testing a new transmitter before putting it into service, etc. Also: testing the transfer switch on the generator, tube replacement on the auxiliary rig and many other housekeeping requirements.
Back when a monthly frequency check was required using an outside source, stations did frequency checks, usually with 1000 Hz tone, for about a half hour so that the monitoring service could measure them.
It's called the "Experimental Period". It's used a lot less today with more reliable gear and elimination of certain FCC rules that required regular testing.
