We are terrible and put it in last minute, but that means she can't always go to get the best deals. I'd imagine you can put it in whenever--although earlier would be better. Amy is great.
This is a super busy time of year for them so I'd say put it in now. It's never too early for Amy and crew.
Actually, I put my order in 3 weeks ago for a delivery in 12 days and I asked for a late afternoon delivery. Unfortunately she was all booked up for the afternoon and my groceries are coming in the morning. That's fine by me because they can just go to Bell Services until the room is ready.