It is spelled 'till. An apostrophe is needed because it is part of a word- until, 'till. .
It is " 'til' ", it comes from the word "until", which only has 1 letter L… . Yes, you DO need an apostrophe. .
It's both because 'til is shortened for "until" but if you look up till in the dictionary, you'll find that one definition is "up to the time of; until: to fight till death." .
It's both because 'til has come into common usage over the last hundred years or so, as a contraction of until. However, till is not derived from until. Till is the older word, in use for about 1,200 years, whereas until is a relatively recent word, maybe 800 years old. .
The older word is til . ( Full Answer )