No, it is 180 days from your first day. Make sure to retrieve your reservation so that the rest of the dates open up. The on-line reservations opens at 6:00 am eastern time. You can "play" a little before your actually 180 day mark to see how it works, but your dates won't be open.
I did all of mine on-line and got Le Cellier, O'Hana's, and Boma with no problems. If you have trouble, you can always pick up the phone at 7:00am. Also if you try to make the most popular ones for later in your trip, you have a better chance of getting it.
Keep asking questions if you need help.