For both a pure and corruption route?

Pure route will naturally be significantly more pressed for time given blessed water quantities and corruption build up, but what about corruption?

Assuming we're spending it, (and especially acquiring 2x through pink scenes) what kind of timer are we on?

I'm a chronic game-restarter when I learn knew things that can optimize playthroughs, but the amount of days we have is still a rough mystery to me, and it matters a lot in deciding how I want to play the game moving forward. Is there realistically time to learn every skill, read every book (especially when Aura learns useless knowledge) so on and so forth?

Are the demons post day-100 actually as impossible as I've read? Do I really need to aim to take them down by then, or can I more leisurely prepare for them and win those fights even when they're more difficult?