Depends on if meeting the characters is important to you. If it is, then as others have said above, 60-90 minutes after being seated.
If meeting the characters isn't important to you, then your family can easily be in and out of there in 30 minutes or so after being seated.
We haven't done a dinner there in years, but we occasionally do breakfast. Our son is past the age of giving a flip about characters anymore, so we can easily do a PPO breakfast there in 30 minutes.