I'm dumping my coins when it's becoming useless no update, no exchange no volume if I am late in dumping my coin then I be in a loss nobody wants to be a bag holders of dead coins even if it comes from airdrops so if I notice that things is not doing good in a coin I'm holding I will be ready to dump it anytime to cut my loss.
When there's no update, no exchange, it's already too late for dumping, you will not have where and you will not have to whom to sell. You do it on time or you end up with worthless coins your wallet. I dump coins when I get the first red flag from the project team, or their community, when I see anything is not on time, when they use their first excuse I dump all I have.