When to order invites/save the dates?

In my opinion, it doesn't hugely matter when you order them as long as you can get them in a week or two before you'd like to send them out.

I would advise against ordering them TOO soon, maybe don't have them longer than a month or so, that way you don't have to keep track of them for as long.

We got ours a month prior to sending, because our calligraphy girl needed 2 weeks to write & we wanted an extra week to stamp & fill. Our save the dates went out 10 months in advance and our invites 3 months.

The other issue with ordering too early is that even small details may change that will result your needing to reorder -- a huge waste of money. Most online vendors can deliver in about a week (e.g, Zazzle, etc.), so other than giving yourself enough time to get them addressed, don't do it too early. If you'll be working with a small stationery vendor for specialty papergoods, check with them for their recommended ordering schedule.

We sent our STDs about 11 months in advance and we just finished sending out invitations 4 months in advance.

Both early, I know, but we have lots of travelers and our date is 3 weeks before Christmas. So the earlier the better.