from the little experience gathered over a period of years in the ICO and project promotion phase and after it enlists in an exchanger, the best idea is to buy the tokens when it gets to the exchanger as the price gets to reduce too and makes a better buy opportunity to the prospective investors. just my opinion though.
It is better to wait until the price falls to its minimum and when it starts a gradual increase, buy it, so at least it is clear the project is not doomed to death, and if you buy at once, the probability of losing all the money invested is too high