By "it", I assume you're talking about his penis.
Whenever sperm comes in contact with a vagina, there is a chance of pregnancy.
Doesn't this belong in the ttc forum?

Nope, it belongs in the I need sex ed forum.

There is no set time. A penis in contact with your vagina means potential pregnancy.
Pre-cum or no pre-cum if he pulls out or not if a penis is in contact with your vagina there is a risk of pregnancy.