Hi Samuel! Welcome to the Disney Parks Moms Panel!
I bet everyone in your party is thrilled to be
visiting "The Most Magical Place on Earth" soon! It sounds like you have done an excellent job of planning the details, all the way down to FastPass+ and Rider Switch.
In my personal experience, the Cast Member in charge of
Rider Switch at an attraction asks if those in your party have FastPass+ or are waiting in the Standby line. If the first party is waiting in the Standby line, the Rider Switch return time is usually the current wait time minus 10 minutes (like the example you gave in your question). If you all have
FastPass+, however, our experience was that the return time with Rider Switch began only 10 minutes later. This may vary a little depending on how busy the attraction is at that time, but for us it was timed well, so that once the first party completed the attraction via the FastPass+ line, the second party's time to go was right away. We spent very little time waiting around!
I hope you enjoy every moment of your upcoming vacation, Samuel! Please let us know if you have any other questions.
Tabitha