Ours was about 9 months, but I agree less time is very managable if you're a go with the flow type. If someone is very detail oriented and has a set-in-stone vision of what the wedding is they will probably freak with not having enough time.
I agree with Mandy, there are a lot of decisions you can make in 1 day or so. When brides have 1 year+ to plan I think more anxiety is created because you spend too much time pondering instead of making choices. I could have done mine in 3 months because I also let the WC do her thing. I did a few extras (so not necessary) and basically just planned on showing up!
Some guests will need more of an advanced notice to attend than others (scheduling, finances, etc.), so consider that.