They are scheduling them from 4-7pm since the CMs usually allow entry to MK at 4pm on party nights. People who do this have regular tickets linked to
MDE and are using one of their allotted days to schedule FP+ for the party day. Then, they use their party ticket instead of a regular admission at 4pm but still get to use their FP+. Then they can use their regular admission on another day later in the trip or so and book FP+ after the party is over. Its kinda a work around the system, a loophole if you will. They need to fix it so park entry is required in order to use FP+, otherwise I honestly feel that this will see a lot of abuse.