Understanding days? Lightning Returns: Final Fantasy XIII

I want to make sure I defeat a certain 2 bosses before they power up my timer days 6 days I know one powers up at day 8 so as timer goes down how do I know when I'm on day 8? Is it day 8 when I extended the timer by 2 days so it says 8 days remain by doing main quests or if I let the timer run down? So if it said 1 day remains will the bosses be powered up or normal? Sorry if I sound dumb for some reason this is confusing me.

In the menu (press Triangle or Y), you'll see that it tells you exactly what day it is next to the clock.

So when something powers up on day 6, it'll power up on the day after day 5.

Also, the days don't change at midnight, they only change at 06:00, when you get transported to the Ark.

I see thanks didnt see that it said what day it was in the menu. Really enjoying this game more than I thought I would the whole XIII trilogy games are all so different in a good way.