Hi Elizabeth!
Disney's Wilderness Lodge does indeed share a bus route with the Grand Floridian and Polynesian Resorts. These buses operate promptly and frequently so you'll find that you're able to get in to the parks without much noticeable delay at all, ready to jump right in to all the Magic!
In the case of Morning Extra Magic Hours, buses will begin operating 1 hour prior to park opening time, just like on regular park days. Since Wilderness Lodge is the first stop both on the way to and from the parks, I'd recommend that you plan to be at the bus stop early to get the first available bus in the morning. For example, if you're heading to Animal Kingdom for 8am Extra Magic Hours, plan to be at the Wilderness Lodge bus stop by 7am. Once you've boarded, the bus will make its two quick stops at the nearby resorts, and then make a straight journey directly down to the Animal Kingdom park!
When heading to Magic Kingdom for the day, keep in mind that you do have a second transportation option available to you. Exit through the rear of the resort's lobby and down the beautiful pathway to the boat docks. There you'll board a Red Flag Boat which will take you over to Magic Kingdom. Buses are also available to Magic Kingdom as a second option.
Wishing you a Magical time at Walt Disney World Elizabeth!
Kirsten