I think there are many strategies in buying bitcoin. Buying more is currently the main strategy or you could say the main goal of someone in accumulating bitcoin. But you can't predict the market. Because of this, there are many strategies for accumulating bitcoin, such as short-term trading, futures, or DCA like what El Salvador does.
Accumulating Bitcoin and selling it when the price is higher is the most suitable option but I think future trading is not a better option and in case of Bitcoin it is very risky so one should either accept DCA method or they should buy or sell Bitcoin according to short term trading but this buying and selling should be according to the market changes.
Now the better time is to buy more Bitcoin and hold it either for the short term or for the long term but don't hold so long that you miss all the important days in which you can earn huge amounts of cash with your investment.