Book at the 180 day mark. I was able to find a time, even though some were during off hours, for every day when I was looking. (This was for end of Aug/early Sept).
And then, like others said, keep trying and play with the times and something might come up. Some people may cancel at the 45 day mark, so you never know when something will open up.
If you can make your reservation at 180 days at 7am you should be able to get one. I have never been shut out when booking Le Cellier at the 180 mark. Good Luck