Dictionary.com does say it's not a word, you're right, Ratter. But that's because it says the real word is til....
Of course, it really depends on the dictionary you use. I still like 'til, just because when you shorten something, you have to put an apostraphe. For instance, if my character is one of those slang-speakers (And I do have a lot), him becomes 'im, them becomes 'em, and becomes an', and so on and so forth. Until would become 'til.
