You might be cutting it close and here's why:
1. The opening ceremony begins 5 min. prior to park opening (@ 9 a.m. that day). This will theoretically leave you with 15 min. to get to GF. Disney recommends arriving 10 min. early for dining reservations.
2. You'll be at the mercy of Disney Transportation. As a previous poster mentioned, the boat would be your safest bet. If you'd pick up the Resort monorail line @ MK, here's what those stops look like: MK->CT->TTC->Poly->GF (and the cycle begins again).
3. I believe there is a 10 min. grace period before you're considered a "no show." At 1900 Park Fare, "no shows" incur a $10/person fee.
I just checked the Disney Dining Reservation site, and found a 9:35 a.m. @ 1900 Park Fare (I based it on 4 people). You should not feel as "rushed" to make that time from MK compared to an early time.
I'm not trying to push this next option, but it's an option non-the-less: eating inside the park, either prior to park opening or after, or making your ressie @ 1900 earlier. There are numerous times available at Cinderella's Castle & a 9:45 a.m. @ Crystal Palace (a $2.13 difference for adults & $1.07 for children). Also, there are numerous times available @ 1900. Just a thought!
Enjoy your trip!!