Hi Christine!
Thank you for bringing your question to the Disney Parks Moms Panel!
The amount of time I recommend really depends on which Walt Disney World Theme Park you are going to. If you're going to
Magic Kingdom Park, you will actually park your vehicle at the
Transportation and Ticket Center and then use the monorails to get to the park entrance. This takes a bit longer than other parks, so I would plan to arrive there no later than 8:00 a.m. You probably won't need that much time, but it will be crowded as everyone arrives for park opening. There is a welcome show at the Magic Kingdom called
"Let the Magic Begin". It takes place in front of Cinderella Castle.
If you mean Disney's Animal Kingdom Theme Park, Epcot or Disney's Hollywood Studios, the timing would be different. Parking for these parks is at the entrance, so you can walk or take a tram. For those, I would arrive at least an hour prior to your dining reservation. I am not aware of any welcome shows at those three parks. You can find a schedule of events for all the theme parks on the
Walt Disney World website's interactive calendar. I hope this helps! Please let me know if you have any other questions as you plan.