The best time to invest in ICO's is in presale or private sale as you get bonus there. But do keep in mind that more bonus is not good for the project. Like 30 or 35 is good.
Yes that's a good advice because having pre-sale or private sale when you invest an ICO can possibly give you a good profit but sometimes we cannot accept the fact that it is closely to be at risk you just have to be more observant in such cases.
If the project seems really good then invest at presale, but if you still in doubt better invest when the project already succeed or when it is already in exchanges. I do invest only on ICO when the project offers something to investors that is not applicable when only bought in exchange.