When trying to get a specific enchanted book with a librarian by breaking and re-placing a lecturn, you can continuously cycle at any time of day.
New world generated in snapshot 20w45a, playing survival on normal difficulty
MC-205014
You can cycle a villagers trade at any time of day
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Hey there!
Just to let you know, this is an intended feature. Upon breaking and replacing a lectern, the villager will lose its profession and gain it back. This causes the trades to be changed each time you do this. To add on, this also works with every other type of villager profession. Hope this helped clear the confusion. 🙂