If you plan to never sell your BTC, well, you are fine to buy whenever you want to. Just buy and hold it. But that doesn't make sense at all of course.
So, if you are a DCA follower, I think you should first select how long you are going to follow the strategy. 5 years, 6 or 10 years or more. If the target is to follow the strategy for a longer range, there's no meaning of having to time the market. But if you are following for say 4 years, you must sell the tops if you are in good profit.