I think that one day of the month you CAN have a cheat day, unless you find that it repeatedly causes you to backslide into days or weeks of off-plan eating.
Now that I'm on maintenance, I myself two "celebration meals" a week. If it's one meal, I'm fine. If I let it turn into a half day of bingeing, I gain. What I consider a Celebration meal is one appetizer, one main dish with sides, a drink, and a dessert.
I did not do these meals until I reached my goal weight. It would have been ok to do one a month before goal, but it would have taken a bit longer to get to goal.