The time to buy will depend on how you view or predict the price move in the near future. If you see that the price to move up in the near future, then it is a good time to buy. However, you must have the knowledge to predict or analyze properly. At least, you know how to read the price chart history. This is one of the ways to predict crypto prices, reading the charts of the prices in the last few days/weeks/months.
It can be very helpful.