Please see this guidance on usage free the Oxford Dictionary:
"In most contexts till and until have the same meaning and are interchangeable. The main difference is that till is generally considered to be the more informal of the two, and occurs less frequently than until in writing.Until also tends to be the natural choice at the beginning of a sentence: until very recently, there was still a chance of rescuing the situation. Interestingly, while it is commonly assumed that till is an abbreviated form of until (the spellings ‘till and ’til reflect this), till is in fact the earlier form. Until appears to have been formed by the addition of Old Norse und meaning ‘as far as’ several hundred years after the date of the first records for till.