How does two turn notice work?

Hi Guys, how exactly does two turn notice work?
If I notify before my turn that I'm giving notice, I take my turn and then once my opponent takes his turn then the truce is over? Or is it two cycles of what I just described?
If I notify before my turn that I'm giving notice, I take my turn and then once my opponent takes his turn then the truce is over? Or is it two cycles of what I just described?