I think there are simply not that many uses for nails in emergency situations.
Using nails as intended:
If you want to build shelter or other wooden constructions you would need a lot of nails - which are heavy.
Hammering in nails with a rock is rather annoying - and you're not planning to bring a 500g hammer, are you?
In any case, for shelter and tool ...
The adequate minimum is 1-2 minutes (100C water at the sea level). Mind the altitude. To kill bacteria you need a combination of temperature and time. At some altitudes (miles), without a pressurizer, you just can't kill some resilient strains in a reasonable time (low boiling temperature). Use other disinfection methods in addition.
Why no less?