They have the same meaning, thus they're interchangeable.
Here is the fully 'story':
The status of 'til versus until and till is often argued about and most style guides have something to say on the matter.
The most common belief is that till is a shortened form of until. You can see how this could have grown up, but the truth of the matter is that till is by far the older word, being recorded from about the year 800, while it took another 400 years for until to appear in the language (it's a compound of till with the archaic Old Norse und, as far as, which also survives in the archaic unto). But the first sense of till was to, as it still can be, for example, in Scots and some dialects. Though the modern sense of till in standard English is always connected with time, this only appeared about 1300.
The current position is that until is the more common of the two words and is generally considered to be slightly more formal, which is why it turns up more often in edited prose. It is also rather more likely to appear at the beginning of a sentence than is till. But till is perfectly good English and the choice of whether to use it or until is often decided by the rhythm of the sentence.
'til, has been created within the past century by people who believe that till is an abbreviation of until and want to mark it as such. It has often been said by style guides and dictionaries that it's a mistake and it arouses passion in some people. Most recent writers on language prefer to describe it as an informal version of until — it often turns up in newspapers, advertising and song lyrics, for example, and in informal set phrases like "shop 'til you drop", "It ain't over 'til it's over" or " 'Til we meet again". But to use the spelling til without the preceding apostrophe is still regarded as wrong.
Courtesy of
http://www.worldwidewords.org/qa/qa-unt1.htm
