Hi Angie,
Welcome to the Disney Parks Moms Panel! Having just checked, I can assure you that Mickey and Minnie Mouse are delighted to hear that your granddaughter is coming to visit them at the Walt Disney World Resort for her first trip!
If you were to arrive late to a dining reservation, you certainly would not be the first! Navigating the theme parks and resorts can be challenging, especially with an infant in a stroller. When we have been no more than 15 minutes late, the cast members have been gracious and still seated us. On one occasion, traveling with extended family, we were 20 minutes late and felt lucky to get seated. The restaurant was crowded but the cast members found a place for us. After that experience, I made note to never arrive more than 15 minutes late if possible. At times, however, you may experience transportation difficulties beyond your control. If that happens, just speak to a cast member at the restaurant. In our experience, cast members have always done their best to assist us.
Now, we are usually early. Although arriving early will not always help (
Cinderella's Royal Table, for example, would not check us in super early), sometimes it does. We always arrive to California Grill at least 30 minutes early so that we can request a window table. They have typically seated us within 10 or 15 minutes. Even if you have a dining reservation, you may still have to wait a few minutes to get seated. If you decide to cancel a reservation, check the restaurant's cancellation policies. Generally, you can cancel up to 24 hours in advance.
Angie, since this is your granddaughter's first trip, I hope you have considered
Memory Maker. Your photos will be priceless!
Magic, memories and Minnie Mouse hugs,
Donyell