I agree with what Jeff said about practicing in shorter intervals. Something you might want to try is to do the physical playing for a short time each day (until you build up the callouses) and then devote some time to learning music theory. That way you are still progressing with the instrument in general and not left feeling like you didn't make any headway or learn enough for the day. And even after those callouses build up, I would try to keep up with learning more and more music theory as you progress with the physical playing. It will make you a stronger player.