Curfew
Similar to a booty call, but a more tactful euphemism in a committed relationship. When the maximum allowed time has passed without having sex, either by appointment or by arbitrary desires. Should be looked forward to in a healthy relationship.
1a. "You've been out there all day, it's time to get inside!"
1b. "Sorry guys, I gotta go- it's my curfew."

2. "I better be upstairs and naked by 10 tonight or I'll miss my curfew!"