Personally, I have never seen any projects list their tokens on exchanges before ICOs. Because they have to pay a lot of money for listing tokens as well as traders maybe trade tokens at the price below ICO price (that I assume these are really potential projects and investors believe in the success of projects).

Due to under pressure of FUD when they delay time of listing exchanges, I think they should list their tokens as soon as possible. But they should choose a well-known or trusted exchanges, because listing tokens on sh*t exchanges will make a big dump of tokens.