There are a few different schools of thought when it comes to hand conditioning.
Most people have probably heard of “Iron Palm in 100 days.” and are thinking “cool, it will take me 100 days.”
Other people have said that you must practice every day for a certain amount of time (100 days, 150 days, 6 months, whatever), and they say that if you miss a day you have to start all over!
A few sources even say that not only must you practice every day, but you also must do it at exactly the same time every day.
Now think about that for a second. How would people in the past have known when it was exactly the same time as they practiced yesterday? Did they have watches with second hands? I don’t think so.
Those are just scare tactics designed to encourage students to be consistent in their practice.
Now, when you are first starting, consistency is important. If you practice once a week you probably won’t make very much progress. If you practice every day for the first hundred days you will probably make much better progress (provided you don’t overdo it and injure yourself). If you miss a few days here and there you are probably fine. In fact, your body could probably use the extra recovery period. On that note, if you have to miss a training day, it’s still a good idea to do the massage portion of your training anyway, if possible.
Some advanced practitioners have said that, once you attain a certain level of conditioning (usually after a year or two), that practice becomes more about maintenance rather than increasing your conditioning. In these situations, you can take a day off here and there without any ill effects. Some people may even say less is more. Do not stress if you have to take a few days off from training. You didn’t develop your conditioning overnight and you’re not going to lose it overnight, either.
If you have to take an extended period of time off, remember to resume training slowly. For example, if you’re used to doing 50 strikes a day on the gravel bag (a number I just arbitrarily chose, not a recommendation), and for whatever reason you had to take a week off, don’t jump right back in where you were. Of course you know that you should warm up with the mung bean bag anyway, but maybe instead of doing 50 strikes with the gravel bag, you do 20 your first day back, then 30 the next day, then 40, and then 50.
Remember that it’s not like one day you don’t have iron palm and the next day you do. Conditioning gradually increases over time. And conditioning also decreases gradually over time, which is why it’s just fine if you have to miss a few days here and there, especially when you’re reached more advanced levels of training.
So if anyone is telling you you have to do it every day without exception ever, at the same time every day or you have to start over, or anything like that, they’re probably either crazy or just trying to scare you into good training habits. Of course, consistency in the beginning is important, just remember not to overdo it. A little bit every day is much better than too much one day and then an injury recovery period.