How often does daytime clenching turn into nighttime clenching?

My dentist noticed that I’ve been clenching at my latest cleaning (and I chipped one of their fillings) and recommended me a night guard. Problem is, they are charging $900.

Now, I noticed independently that I had been clenching. I started after getting a crown last year. I guess it adjusted my bite in some way and I clenched for comfort. Eventually my jaw became sore and I started getting headaches. My dentist confirmed that the clenching was a new phenomenon and wasn't present when they did the crown.

Now, I am not opposed to night guards, but I have stopped clenching altogether. I just... stopped. No more soreness or headaches. But that is during the day, I don't know what happens at night. Is there a chance that I'm clenching at night?

I've been shopping around for nightguards but everyone requires a cleaning beforehand. I guess the crux of my question is if I can wait until my next scheduled cleaning in a few months to get the nightguard? With the hope that the damage was from daytime clenching.