We also had a no attack for 10 turns rule in NvV2, which was thoroughly abused by the vets to destroy one of the players' potential economies.
As far as NAPs go, most tend to require 3 turns before hostilities can commence. But I've signed an NAP 10 before (never again), and shorter ones occur as well. Generally these are based on the needs of the individual nations. For the record, as some of you seem to be thinking of NAPs as quasi-alliances, I don't think that most players think of them like this. Whatever the case for this particular game, you should go into most games with the expectation that, at some point, the guy you have an NAP with may try something funny even if you are still under the NAP. Usually you will not get attacked under the flag of an NAP with no warning, but there are players who will ignore this even in binding diplo games.