If time passed while reading the in game books, it would put some fear/reluctance into reading them in dungeons, and give some added value to the 10 septims you occasionally pay for a room. This would be especially handy for those times when you have the extra dark nights mod running and you don't want to go out into the wilderness after sunset or before sunrise, and hate just waiting or sleeping for too many hours. So I'd like to be able to sit in my room at the inn and spend some time reading a book I brought with me, or one they have in the room already.