I don't think anyone knows exactly when is the best time to buy bitcoin. some people would say buy when prices go down and sell when prices go up. in my opinion this is easy to say but it is quite difficult to do because the price of bitcoin is very volatile. so that I am principled when I have more money I will buy bitcoin and then hold it. I will hold it until the price of bitcoin can pump higher than my purchase price. I will be patient waiting for that. investing in crypto does require patience.
I agree on that, there's no one can knows when's exactly the best time. But we use indicators and speculations and create an intelligent guess when it is the good time to buy base on the charts that we see and specially if you're into analysis. There's also that practice of cost averaging that no matter what's the price, buying is a must. And for those who don't know when's the exact time to buy, they can do that strategy.