I think the best time to buy is today because bitcoin starts pumping , then next buy is when it goes dipper below 20k$, the next is when it touch down 15k$. For me buying in 3 stages is an advantage and a good strategy to earn never invest all your money directly because price is high on volatility you will surely get bored or discourage if you saw your investment down in one blow.
Some people are just then about to realize to buy when seeing the market in green and major coins are pumping. Many are quite hesitant during the crash but they preferred but at a higher price.
If we only have a bright vision of Bitcoin, it is possible we do move and take action during the crash but yes, we dare not and keep negative as well thinking it drops more rather than seeing this as a chance to fill our bag. Sadly, the idea isn't great, we always miss the bottom.