A 52 Week Reading Challenge I created late last year to challenge myself in 2021
Technically the rules are that one book can only count for one challenge and you have to read the book in the corresponding week. I've personally already adjusted the rules:
1. Fulfill challenges corresponding to a month in that specific month (January: Week 1, 2, 3, 4)
2. Fulfill challenge until that specific week (Week 3 book can be read in weeks 1, 2 and 3)

In general, just fulfill the challenges whenever you want to. Reading is supposed to be fun and not stressful.