Is 'in a week or three' correct English?

The other day I had an argument with a fellow translator of English about the correctness of the expression 'in a week or three', which, in her opinion, is incorrect and may even be described as 'Dunglish'.

My gut feeling tells me there's nothing wrong with it, and any advice from native speakers of English would be highly appreciated.

As stated in the comments, there is nothing wrong with the phrase. It is uncommon and has a specific use. It is a modification of the common phrase, "in a week or two". Its intention is to mean the same as its root phrase except the anticipation will make it seem longer.

It is also used in a derogatory sense when an entity frequently over promises on delivery schedules.