Since cryptocurrency prices can often be quite volatile, we offer a 60 minute timeframe for which your sell order will remain open and for your coins to reach us.
Sending coins from an exchange and selling them to us is not against our terms and conditions, however, exchanges are notoriously slow at executing withdrawals. Unfortunately if the 60 minute timeframe has surpassed and we have not received your coins, your order will be cancelled.
We therefore recommend sending coins from your own wallet. If you click the link you can find information on how to download or install your own wallet.