Yeah, 8 hours of essentially uninterrupted time is a lot to ask -- in fact it would basically be a deal-breaker for anyone with full-time commitments, or who otherwise values their time.

Also, (explicitly) timed coding tests imply that you don't really trust the candidate. Of course they could be lying when you casually ask how much time it took (or whether they got any help), but the few who go that route will probably quickly test out your other filters.

The trust signal, meanwhile, takes a lot of care and consideration to cultivate -- and shouldn't be discounted lightly.