Well, clearly your opinion has developed since your first response, as you can't staddle both 'this is a normal part of parenting, suck it up', and 'this is obsessive and unusual behaviour'. So, what would you recommend now that you're enlightened I have an oddball as a daughter?
I was loose in my description of the two-hour incident because it was an off-handed reference and I didn't expect to be so thoroughly interrogated about it. She doesn't tire of books, even when she's tired. That was the point I was making; she's always interested in going round again. Shock horror, when we tested the limit and found there wasn't really one, it took time to wind her back down, she was up for over two hours past her bed time, purple-bagged, and still willing to read. We did not tease her by taking it away, watching her cry, and then reading again; once we were done, that was that. We did not read the book without so much as a toilet break for the entirety of the two hours. This was a bed-avoidant issue that has been addressed and fixed, but was an example of the fact that there was no 'just read until she gets bored of that book'. She didn't. I can't give you a an exact time for how long it took to figure that out, but I can say she was awake for two hours past bed time as a result.
She is happy and respectful of boundaries, boundaries that I had to set because she wants to read more, not because she will tantrum if we don't. She's a thoughtful and empathetic soul. She will ask, every time, 'read one more?' after the alloted two reads, and I will say 'No, we'll read this one later', then she will bring me another book, and another, until I say 'no more books right now, would you like to do X instead?' and she will oblige, but you can bet she's bringing me the first book again within the hour. She would keep going if she thought I would.
This thread isn't about her behaviour, she's a delight and I'm not concerned about her. What I am concerned about is that by reading the same books a minimum of eight times a day (X2 before breakfast, after lunch, before dinner, at bedtime on a conservative day), I read the same book a minimum of 108 times a fortnight. I get bored of the book, she's still really into it, what do I do about that? I don't want to get visibly agitated by 'Dear Zoo' on read 75, because she picks up on that, and I don't want her to associate reading with something negative. There are some books I can tolerate longer than others, but none that I can tolerate as long as she loves them. It's a shame, and I want to do right by her. I don't know if 'right' is setting boundaries or sucking it up and doubling down, just getting better at autopilot without engaging as intensively to placate her. The question is about my approach, not her being interested in books a little too much. You're way to hung up on the bed time thing; we trailed something, it didn't work; she loves pigeons and playing and bubbles, she just loves books and letters more.