Bad idea to sell Ethereum lots after an ICO. Big sales cause price drops which makes more selling by others. Only cause more price decline. Better to sell little at time or just hold since price is lower.
theoritically if the market cap of eth is big enough, ICO sell-off should not have significant impact on the price movement unless they raised huge.
However, i think most approach (legit ICOs) will be selling off eth as and when they need the funds for the project. dollar-cost-averaging is always the best approach.