Peace period

i have joined a game with a 3 day peace period for human players only not for AI

day one there are many open spots for more to join

My question is what if i attack a playable country controlled by AI is that allowable because they are AI

Second question is what if after i have launched against playable country and next day someone joins in as that country

do i have to stop my attack?... do i get some penalty?... or am i allowed to continue my attacks?