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.
yes it is really difficult to decide whether it is good time to buy or sell, because sometimes the after buying at low the price comes down more and sometimes after selling at high the price increases much more then people regret that it was a wrong decision, i think to avoid these regretting we should set our own targets, like when there is bull run then we should buy more and more, and when we reach to the targeted profit then we should sell it without any delay.