The best time to buy bitcoin, if they have more bitcoin in your wallet then if they see the price is high then no more doubts to buy for it.
Today is the best time for buying bitcoin because the price is below $8000 and with the passage of time it will grow again and very soon it will cross $10000. If I have money I will buy bitcoin today because I think it is the best and easy way to make money while doing exactly nothing just holding for some time. Every time is the best time for investment in bitcoin.