Not to worry. I do understand that this takes time, and more importantly that it is your job and not just a hobby. In many ways I believe art to be priceless, because no two pieces can be exactly the same. They are unique, and intimate, in my opinion. Also, I am rubbish at drawing of any kind, so my appreciation is immeasurable.
Thank you for the quote. Size sounds quite fitting, and I'm looking forward to seeing the finished product on the 13th. Do you require a deposit, or payment up front, or is payment on the 13th alright by you? It matters not to me.