A few factors seemed to contribute to that sort of thing here.
He may be at the stage where he isn't as tired as he used to be or more tired & needs a longer wind down & so a longer reading time may be needed. It could also be that he is really liking the type of connection that the book time gives so maybe more of it is needed in the day time as it is something that "fills his Mummy cup"
Sometimes these things are hiccups & right themselves sometimes they are a cue that there needs to be a bit of a change in the routines eg I found that there was a point where the bath was better before meals because it dragged on & hyped them up.