When a Sell Order is created the system will show you an exchange rate which is valid for only 15 minutes. Hence, in order your purchase to be processed, you have to send and we have to receive the amount of Bitcoins you are selling within 15 minutes.
Although it takes around 2 bank days for a Sell Order to be processed and completed, the exchange rate is always locked immediately after your Bitcoins have reached our Bitcoin wallet. This can only happen within the time period of 15 minutes. If we receive the Bitcoin transaction later, the Sell Order will not be processed and the Bitcoins will be refunded.
If the completion of your Sell Order is delayed for any reason from our side like a compliance check or technical disturbance of our system and takes longer than the usual processing time (see above), once the order is processed the exchange rate applied will be the same as the one shown when the order was created.
You can find more information regarding processing Sell orders in the help article "Processing Times for Sell Orders".