Thanks so much for choosing me to work on this project! I'm very excited to get started, but I do want to check with you on one issue first. You've submitted your document with a one week deadline -- would you be willing to extend this to two weeks? 

I completely understand if you need your manuscript back within the given time frame; however, I would like to be able to give you the best editing possible, and an extra week would be extremely beneficial. If you are okay with the extension, I will have the manager adjust the charge and refund you the difference. Please let me know!