Welcome aboard, Jaclyn! Disney Cruise Line's Broadway-style shows are the best of their kind at sea and such a fun way to enjoy time together as a family when you're onboard one of Disney's ships.
A few years ago my family enjoyed a sailing when there were matinees of the show offered, however I haven't seen those as often recently on the itineraries we've sailed. These schedules are always subject to change, but traditionally, you'll find that there will be two show times each evening. One at 6:15 for those who have the later dining seating to attend before dinner. The other is at 8:30 for those who have had the early dinner to enjoy after they finish their meal. If you choose not to eat in your assigned rotational restaurant, and instead have room service or dine in Cabanas or at the quick-service spots on the pool deck, you can attend whichever show you'd prefer that night. There is no assigned seating, so just arrive a bit early to find a spot and you'll be all set.
If a matinee is offered on your sailing, which again, isn't the norm, you'll see it listed in the Personal Navigator, which is the schedule of the ship's events and activities for each day. I hope those details help as you continue to plan, Jaclyn! Happy cruising!