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 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. Actually "untill" with two l does not exist :) I hope I was able to help you. Cheers Martin

They are synonyms. They are all prepositions of time and refer to a period of time leading up to a specific time.Usage sometimes depends on emphasis.Sometimes besides till amd until..'til is also used.But until is regarded as slightly more formal and is more common in written English than till or 'til. Wait till I come. Wait until I come. Shop 'til you drop. In all these examples we are talking about a period of time.The end time is introduced by until,till or 'til. There is also a verb "till" which means to prepare land for sowing seeds.(agriculture)