Hello. First, your usage of the word is incorrect. You would restructure your sentence as follows.
You have until Friday to complete your work.
This would indicate that you must have your work done by Friday.
Secondly, you will need to do more research, but in older usage of English, words have been abbreviated. An abbreviated word will contain an apostrophe, such as the word 'till. Today, the abbreviated word 'till is really more slang than proper English.
You can use till and until interchangeably in both writing and speech, though as the first word in a sentence until is more common: Until you get that paper written, don’t even think about going to the movies. 1 If you’ve always thought that till is a shortened form of until, stop. As prepositions meaning “up to,” both words appeared around 1200; the conjunction till is about 70 years older, with until not being used in this way until 1300. Till itself comes from a very old Old English word til, “to.” Until was formed from till by the addition of the prefix un-, which meant “up to.” So etymologically at least, until is a self-contained redundancy, meaning “up to up to.” 2 The mistaken impression that till is a clipped form also has a few gray hairs. People started spelling it with an apostrophe in the 18th century, indicating they believed it to be a shortened form of until. Although ’till is now nonstandard, ’til is sometimes used in this way. It is a modern invention, dating from 1939, and is considered acceptable. But why bother with apostrophes when you can do without?