I agree with OGM, but some are more secretive than others. Each chicken is an individual, especially with behaviors it’s hard to paint all of them with the same brush. In warmer weather I’ve seen a broody leave her nest twice a day and spend more than an hour off the nest each time. She spent a lot of that time hanging around with the rest of the flock. I don’t see that often.
In cooler weather I’ve seen a hen stay off the nest for fifteen minutes, rushing everywhere and not being real nice to any chicken that got in her way. That’s the behavior I’m more used to with a broody. Often I never see a broody off the nest. But since she is not pooping in the nest, she is leaving. I just don’t see her.
Different people do this differently, but I leave my broodies alone until she brings the chicks off the nest. I do check under them every day after all eggs are laid to remove any I haven’t marked as belonging, but other than that I try to be very hands-off.