If having Bookbinder buffed the effect is calculated for entire production time, not taking into account if buff expires before production has been completed - how it works for Barracks and Provision Houses...
My Bookbinder is level 6 so normal production time for a Tome is 12 hours, with 'Hide Glue' added time is stated as 6 hours even though buff will end in 3 hours; correct production time should be 12h-3h = 9h.