Each of these words means "up until the time of," "near or at a specified time": "We shall wait for you 'til (or till or until) sundown." "He did not arrive until (or 'til or till) yesterday." 'Til is a shortened, variant form of until. 'Til seems needless, is obsolescent even in poetic diction, and should be used rarely, if at all. Till and until are interchangeable; each normally means "before," "up to," or "when." Until is usually preferred over till at the beginning of a statement because of its sound and to prevent confusion. 'Till is nonstandard.
Dictionary of problem words and expressions. Harry Shaw. 1975.