。
I can't get away from work until five.
Literal
I [topic-は] 5 o'clock until work [object-を] cannot-leave.
離れる ('to leave, to get away from') takes を for the place left — 'leave from X' is 'X を 離れる.' まで marks 'until' as a continuous endpoint (not a deadline). 離れられない is the negative potential — 'cannot leave.'