Go to: https://etherscan.io/address/xyz
(where xyz is your wallet address) - search for the eth transaction you sent to EOSCrowdSale. See the age column that shows "days ago" that this was sent. For example "4 days ago"
Now go to: https://eosscan.io/ and see what period we're currently at. If its say, 291, then using above example, subtract 4 from the current period and that should be your claim day (or either side of it)