Giving it a little more thought, if you know the exact time and date that you withdrew then you can check which block that was actively being added to the network at that time. You could then look for the amount you withdrew to see if it shows up at the time of your withdrawal, and if it does, it's been included in the block. Not entirely sure how you'd go about doing that - I'm sure there's a simple way using blockchain.info but perhaps another member can detail the process. You can also view unconfirmed transactions on blockchain.info so if you search for the amount in question it will limit the results and you'll be able to see if your transaction is included in those.