Here DCA method should be done in such a way that you can hold for 5-10 to 12 years. You have to have a plan, participate in more investments, the longer you hold Bitcoin, the more you can improve, because if you look at the present time, you will surely find the solution to all the problems yourself.
Well, you're quite right about the investigation plan duration, bitcoin investment can be sustained above the duration you've mentioned because it isn't just any kind of coin that could dump overnight and AFAIK , Bitcoin has always been a good example of a good investment at large ......
However, on average we could take that duration but even after then total withdrawal shouldn't be done but withdrawal strategies could be use to sustain investment