If one tries to add a recording with a length of e.g. "3" the submission will initially fail:

Not a valid time. Must be in the format MM:SS

The value in length changes to "3 ms" and when trying to submit again it's accepted.

https://musicbrainz.org/edit/63671115

Reproduced on test.mbo:
https://test.musicbrainz.org/edit/3264
https://test.musicbrainz.org/edit/3265