How long does it take your vagina to tighten up after having intercourse?

Not long: There is no specific time frame. This will occur as blood flow to the area is re-directed and tissue swelling decreases. Probably on the order of an hour or two.

Quickly: Prior to menopause, the vagina should have very good tone and quickly return to normal size opening following intercourse. After menopause, the return may be more gradual due to decreased tone from lower estrogen levels.