Overnight means exactly, how it sounds. Multiple hours, usually over 12 hours.

Every girl is different and no one has set rules for it. Everything can be negotiated. Usually man get a companion to hang out with him - dinner, drinks, socialization, BCD time in the evening and sexy morning.
Or it can be all day date. Or multiple days.

People who desire extended dates like overnight, are not penny pinching and usually are not worried about stay up all night to get your money's worth.

i hope it helps.