Lol, I'm starting to think I'm gonna be screwed. Still in chapter 3 with less than 4 days left, this chapter has been taking awhile. No biggie though.
To the people asking, it'll work like any other DR where progress is always saved and kept over. You could just straight up spent one entire cycle of the game exploring. Get blueprints, find tragic endings, level up, etc. and that just makes an actual playthrough easier and faster as you'll be more powerful and have more weapon options.
It is however super misleading how they talked up the game. Not having an actual time limit on the main missions to have them expire yet still have it all tied to a central clock that expires, and side missions still having a normal timer is not how I expected the game to play after the prerelease stuff, haha. I actually backed out of nightmare mode(didn't know where to find a bathroom and the progression of the game just recently clicked regarding that) but it seemed the same there, as the main missions don't seem to ever expire now. Only in there it seemed the clock moved faster in general as I saw the cutscene for night time a lot sooner.