I think the key is to start out with a shorter time, then do it regularly and build up the time. This is what I needed to do when learning to play guitar and clarinet. If I played too much when I hadn't played for a while, my fingers would get so sore from the guitar strings. After a while of regular play, the tips would callous up. For the clarinet, it took me a while to strengthen up my lip muscles and breathing muscles again. I also agree that metal thimbles are hard to use, I do have one that is leather and works for me better but I still mostly bind by machine as I really think that is stronger as well as faster.