How long does a trip need to be for Cryo?

Aliens floated the idea of a 17 day trip for the Marines. Covenant after their Cryo incident opted to stay awake to approach the planet. So where is the cutoff? I know air and resources factor in but the expanded universe if I am remembering it correctly from a book adaptation implied you go a bit nutty at FTL if you are awake to view it. However the Nostromo apparently runs about 0.4 Light Years a day and they were clearly going FTL and awake. I know a deletef scene discussed air and resources being based on them being out only for a limited time.