I’m finding it rather frustrating to try and find a path through this game, given the timed text and the inability to save. But on top of that, the walkthrough doesn’t make sense to me – and I feel like I’m just missing part of the interface or something. The walkthrough tells me to read books to obtain rewind tokens. Now I can obtain books just fine, but this just gives me the message:
and there doesn’t seem to be a way to actually read the book. Any hints?
It turns out you can open up a menu with the Escape button. I wasn’t expecting that, but this probably solves some of the problems I described above. I’ll try again!
Oh, that actually opens up a completely new part of the game! 
I have been replaying this game again and again, for almost two hours now, trying (and failing) to get to the optimal ending. And it never once occurred to me that I could press Escape to get a menu where I could actually read the books, journal pages and fragments. Yes, it is mentioned in the Controls submenu, ‘Esc: Open Menu’, but I just thought that was a shortcut to get back to the main menu.
I liked the game, but it really needs to make stuff like this (the book reading feature and the save & load feature) much easier to discover by the player. ‘Hidden’ keyboard shortcuts for crucial game elements isn’t a very good idea.