This is theoretically true but it’s also rife with misaligned priorities. The people putting together these take home assignments have little incentive to ensure that they can be completed by a competent engineer in the allotted time. The engineers completing these assignments are definitely incentivized to underreport how long they spent on the assignment.
With AI coding this is also largely useless. These “build this thing in 4 hours” assignments come with a literal prepared prompt so that they can be churned out in 10 minutes.
We don't ask or check how long candidates take. You're a professional, we give you a challenge, you can decide (up front, 30 minutes in, whatever) whether you're likely to be able to finish in the budgeted time. Maybe you can't because you've got a lunch date and don't have the contiguous block, and want to do it in chunks. Fine by us.
Again, the underlying smuggled premise here is that candidates have to finish the work sample. No they don't. In fact, that's a strong sign it's not an effective work sample. A test that everybody passes isn't a real test; it's just a hazing ritual.