If you plan to list your token/s in the crypto exchange/s , I think it is better to do it after the ICO period is over. It is better to have it at the end of the ICO, for the reason that investors will buy token/s in the management itself. There are times that investors buy tokens in the exchanges even the platform/s is/are having the ICO period, it is not a good practice because the management will not get enough sufficient budget to runs out there platform in the future.