Welcome to planDisney, Kris!
Park hopping generally starts after 2:00 pm, but you are correct that the only time that you can not park hop after this time is when the theme parks are at capacity.
I will be honest with you and tell you that I have only ever heard of the parks reaching capacity for park hopping one time! And that was on the evening of the 50th anniversary of Walt Disney World Resort. I was there that night and I can assure you, I have never seen it that crowded. Everyone wanted to help Mickey and Minnie kick off the celebration.
In fact, it was such a rare occurrence that a
My Disney Experience Mobile App notification was sent to every person with a
Disney Park Pass system reservation for that day. So, I really don't think that this will be too big of an issue for you. Even if you can not hop to your desired theme park, I am fairly certain you will be able to visit at least one other park.
Kris,
theme park tickets are traditionally non-refundable.
I hope that this answered your question, Kris!
See you real soon!
Sarah B.