Basic Coinbase question

[chesthing]

I contacted Coinbase but they just don't seem to understand what I'm asking, that or they don't want to answer it. I recently linked my bank account and don't have a credit card, so I have 4-7 day delays for buying/selling up to 10 btc.
Here's my question: if I purchase a btc at current value of $800 but get funds withdrawn 4-7 days later, what do I end up paying for the btc, $800 or whatever the value is when the money is withdrawn from my bank account?
Same question for selling, when I sell a btc at current value of $800 will I end up getting $800 4-7 days later or will I get the value at the time it is credited to my bank account?