I think that it is better to buy immediately after IEO. In addition, it is not always possible to buy during IEO. But most of all profit will bring participation in the beginning. So if you have the opportunity to join in time, then you can do it.
it depend on which exchanges this IEO launched.if in binance ,i think we have to participate early, dont wait it till traded in market or we will loss best opportunity to gain profits.usually price rise alot after trading was open in binance and ofcourse we will get higher price if compared with in early stages.in order to participate in early stages we must prepared and stored native token before its launched, so it has high possibility that we get number to this IEO.