well catching perfect investing time is nearly impossible. however, we can make optimal calculation by using a method that has been already widely used in the traditional investing field such as the stock market.
There is no denial that the price of bitcoin fluctuates dramatically and predicting it can be quite troublesome. But if you have the intention to invest in bitcoin in a long run, I think that it's always the perfect time to buy bitcoin because the price now is pretty high compared to previous years and it will keep going up. So if you can wait, there should be no worries. However, if you want to gain some profit fast, you need to have the knowledge and experience to choose the right moment to buy and this can be tricky.