Blood and Honey- new game for experienced players (running)

[Hurmio]

I'm a bit confused by this NAP thing. I canceled my NAP with Yomi with an ingame message with arrived on turn 17 i guess. It was a NAP + 3, so i assumed it would would end on turn 20 (attack orders allowed on turn 20, solving on turn 21). Now i was attack on turn 20, which, in my opinion, is a turn too early (again). I might be wrong on this, since i've always just assumed that signing a NAP has a builtin "safetime" of 1 round, meaning that i can't attack on the same turn i cancel the deal. Which would mean, that a NAP + 3 grants three turns of peace after it has been canceled.

So am i right or wrong? It's a bit confusing!