OP - Call Stacie Smith at MetroParentRelief - 703-798-0024. You can tell her Elizabeth w/ the twins recommended her. I've used them a few times, as have colleagues, and she is great - very responsive, gets what working moms need, has a pretty good size network of available nanny personnel, and will definitely help you if she can.
They can do just short term individual days, or a longer stint.
Good luck!