tillOr should it be ‘Til? Or neither of those, but rather the whole word: Until?
It’s been said that English is one of the most difficult languages to learn for those for whom it is not their native tongue. Here’s one of those conundrums that just make people scratch their heads – even those for whom English IS their native tongue.
Thanks to the good-natured wordsmiths at Grammar Party for the details on the till/’til/until question. Here’s the case they make for till:

It would follow that till evolved as an abbreviation of until. However, till is actually the older word, being about eight hundred years old in comparison with until’s mere four hundred years. Until came into being as a compound of till, which originally meant to—and still does in Scotland—and the Old Norse word und, which means up to
Since till is the etymological forefather of until, it makes sense that it would be the best choice for a shortened version of until.
 
But, there’s also support for ‘til:
Using apostrophes to replace letters happens frequently in English. Think about goin’ or rock ‘n’ roll. This makes ‘til seem like a natural shortening of until. Besides, since when do we add an extra letter (the second l in till) when we abbreviate words?
Finally, here’s their verdict:

Till is generally accepted as being more correct than ‘til. According to the Associated Press Stylebooktill is the way to go. And, depending on which dictionary you use, ‘til is either an accepted alternative spelling or a spelling error. Despite some sources considering ‘til not technically wrong, it’s best to use till as all sources consider it correct.
And we feel that you can never go wrong with the full and complete UNTIL.
Read the entire Grammar Party blog on this topic here.