Dealing with 15-minute transaction time limits I just started using bitcoin a few months ago. I recently had an issue where I made a bitcoin withdrawal from one account to my deposit address for another account. The bitcoin account where I made the withdrawal took several hours to process the withdrawal. The bitcoin account where I was depositing the money only allows 15 minutes for the transaction before a new address must be generated. So because the withdrawal was processed past that 15 minutes, the money was not credited to my account. I ended up having to email the company with the account I deposited to in order to resolve the issue. Luckily, it was a small amount of money, so the ordeal wasn't too stressful. But I do plan to transfer with larger amounts of bitcoins, so I want to know how to avoid this when dealing with accounts that require payment to be received within 15 minutes after generating a deposit address. 

Thanks :)
It sounds like you are using two different hosted wallet providers.  What you should do is download your own wallet application that you run yourself, and use it as an intermediary between your two hosted providers.  This can be a wallet that runs on a desktop, laptop, or your phone, but doesn't have to be a full node.  You can find a wallet here:  https://bitcoin.org/en/choose-your-wallet

Once you have that, withdraw your bitcoin from the first service to an address from your own wallet.  This may take the usual several hours.  Once you see that the transaction has a confirmation on it, you will be able to then send it to the second hosted wallet easily within the 15 minute timeout.