I like a lot about this. Slowburn corruption, female protag hell yeah.
My one hiccup is that I am not really into having to optimize my playthrough to not lock myself out or if there is a timer. And having peaked at the guide it looks like that is very much the case. At first that sounds like it adds gameplay engagement but in practice that means checking off a guide and removes the game aspect instead, at least for me.
Don't worry about it, you can't lock yourself out of any mental changes. Some H-scenes are missable, but that's mainly relevant if you're going for a maximum-lewdness run, you don't need them to make progress.
And there is no timer, just a slowly-increasing corruption which could, in theory, lead to running out of mental changes and getting a Soul Break. In practice, the passive corruption increase of even a 80-day playthrough accounts for only a fraction of the mental changes you can make. You spend 30 corruption on the two relationship levers alone. The only way you can realistically lose if you use Star Knightess on most of the boss fights.
Also, if you're still having misgivings, you can get someone's save from 3 pages ago and get some NG+ bonuses in the Clear Gem room.