Some companies use a process where the candidate doesn't see the challenge until pressing "start", and then they have x hours to complete it. This seems to be

Some companies use a process where the candidate doesn't see the challenge until pressing "start", and then they have x hours to complete it. This seems to be far superior for obvious reasons: 1) It normalizes the submissions, making the review process more accurate/fair 2) It removes any ambiguity or implication around the amount of time that should be spent 3) The amount of time a candidate has/is willing to devote to an unpaid homework assignment is likely not meaningfully correlated to their ultimate success in the role, but the process described by OP likely over-indexes for that.