What measures does your company have in place to buy bitcoins at the prevailing btce market price when a customer confirms a bitcoin withdrawal since delivery of btc can take 24 hours?

What bitcoin price does the customer receive when requesting btc withdrawals?
A. Market price at time of request
B. Market price at bitcoin transfer ( blockchain registers the transaction) within 24 hour window
C. Daily BTC average price ( Hi+Low/2)
D. Other