Most of the moms I know would not make it out that early on a weekend. Even if you tell them 9:30 they will stumble on in around 10:00, 10:15, even 10:30...rarely does everyone show up at the designated party time.
I personally am an early bird every morning, even weekends, and would be there. A lot of people stay up late and let the kids stay up late on Fridays and then sleep in Saturday and Sunday.
I used to plan a great deal of moms group events, years and years of doing this...and in my experience...even on weekdays a lot of the parents would show up late for those events and parties too even if I made the 10:00 am start time. It's just hard to get out the door, I totally understand that.
And on weekends they sleep in too, go out to breakfast or like to laze around a little, etc. Good luck.
I personally would go with 11 to 1:00 for a party slow or else 1 to 3:00. Even 3:00 to 5:00 is good a lot of times and then you wouldn't have to serve lunch...Lately all the parties we attend are 1 pm ones. Hope that helps!
I would ask the attendees you have in mind and get their input, might as well ask them and then will give you an honest answer so you don't waste your money. Hopefully you have gotten to know most of these parents that you are inviting....