Daniel Cormier says the clock is ticking on a Jon Jones rematch ... 'cause he's retiring when he turns 40 (next March), period.
We got the UFC light heavyweight champ on the TMZ Sports TV show ... and asked if there was any way he'd make an exception for his hated rival -- who could be on the shelf past then 'cause of his steroid suspension.
"If I'm not gonna do it for guys that I really like, I won't do it for somebody that I don't like," Cormier said.