As long as it takes to not make a loss. Usually a long hodling time is rare, but it also depends on the time frame you are trading on. If you trade on the 1 day frame, you will find mistakes can take days to weeks of hodling. But you can usually find a spot to sell at a profit in a short time frame, sometimes within the same day. If you were unlucky enough to get hit by multiple dumps then the worst thing you can do is panic and sell. That is 99% of the reason why traders lose money. I have found it better to just wait.
Shorter terms is a lot harder to handle because it requires a lot more quick action and quick thinking and quick reaction as well. So all of that is a very difficult thing to do and not a lot of people does that, which is why we are seeing a lot of people losing money since they don't do those things quickly.
While we are on the subject, having different strategies could still work, there isn't a single correct strategy in any case, there are some good ones and there are some bad ones. I believe that we are going to see plenty of good ones in the future, and for that to mean something nice, we need to figure out how to get better results as well. I believe that's the hard part people have trouble with, because they try to find that one great strategy.