Not proper but it scans as “wait till”, as “til”, “till”, and “until” are interchangeable in common English, “till” being a somewhat archaic but still often used version.
The preposition till is ubiquitous in informal register of modern English; nonetheless, in formal register it is often replaced with until or to, except in some varieties, such as Indian English. This predisposition is likely influenced by the widespread misapprehension that till is a clipping of until, which it is not (until being an enhanced form of till). The spelling 'til, itself also deprecated by some writers, was born of that same misapprehension.
Just out of curiosity: What do you think 'll is the contraction of?
Not proper but it scans as “wait till”, as “til”, “till”, and “until” are interchangeable in common English, “till” being a somewhat archaic but still often used version.
Interesting
https://en.wiktionary.org/wiki/till