I'm running on a Lonely Planet book, so I know approximately how long the trip will take... it's more a matter of approximately how much time it would actually take in transit after adjusting for bus connections, as well as knowing when approximately we have to leave Kalambaka, or even whether it is necessary to overnight somewhere enroute.
Of course, knowing Greece, my timetabling activities will be an estimate at best anyway. Thanks for confirming what I suspected
(that Greek bus schedules are not easy to find).