Last June it was very busy and we were able to walk in to:
1. San Angel Inn for dinner
2. 50's Prime Time for lunch
3. The Plaza for lunch
Will you be able to walk into LeCellier or Ohana for dinner? Probably not, but with a little flexibilty you should be ok. And defiantely KEEP trying online. We are leaving about the same time you are and this past week I was able to get a 9:00 am breakfast at Crystal Palace (which I was unable to get for weeks).