> It makes less sense in an era when tenure is better measured in months than years.

If a person's tenure in companies is measured in months then they're signalling they're a C by your logic, or is at least raising a red flag to whoever's hiring. I may be showing my age but that sounds wild to me if that's the norm now.

Maybe this depends on the framing? Ex. 18 months is fairly common in some circles, but that could alternatively have been expressed as a year and a half.

6-12 months? Red flag 12-24 months, especially early-to-mid career? Not uncommon