Saturday night Just a contracted form like: 토요일 밤 -> 토 밤

Do you mean 'sad night'? Of course it's not literally...a night can't be sad. It usually refers to a feeling during such a night. It's also use in expressions like a 'sad day' or a 'sad time'. For example, "It was a sad day for the Clintons, first they lost in Iowa and later on Hillary started to cry on national television." Hope this helps.

Having no sentence context doesn't help! But I agree with Fanahan, Francesca & Noor, "sat night" most probably means "saturday night"

yeah I agree with Noor. it means Saturday night (the day of the week.)