Over time the tips of the fingers on your fret hand will actually go through a few stages. Normally they will first be pretty tender and sore, over time they may get worse, after that you will develope a real hard callous which you will have for a while, eventually the apparent callous will no longer be there and your fingers will look and feel normal but will be inherently resistant and you will be able to play for much longer amounts of time with little to no discomfort. This goes from experience, and based on the fact that I played for several hours a day when I finally got serious, and saw other people I taught to play guitar gutiar go through the same thing, I have been playing for 15 years at this point.