Noun
body clock (plural body clocks)
Biological clock.
It's no fun being a broody Iranian woman. Every time I said to people "My body clock is ticking," they would hit the ground! Shappi Khorsandi
If I'm at home for the weekend - and that is almost never - I tend to get twitchy at about eight o'clock in the evening because my body clock is timed to go on stage. I don't know what to do with myself. Jimmy Carr