I think this is more relevant as the day goes on or as you are trying to snag the times that pop-up throughout the day? I'm assuming a certain number of riders are assigned to each
genie+ ride for any given time period.... so say 100 people can book ride XXX from 10-11am. Once those 100 slots are gone it moves to the next time and so on through-out the day. Eventually you'll hit a point where there are say 3 spots left... so when you go to book with a group of 8, it'll move you to a time that can take a party of 8. Or say a group of 4 cancels so their 4 spots go out for someone to book... again, your party of 8 wouldn't work, but a smaller group could snag the time.
We used genie+ after Thanksgiving with a group of 6 and when we were trying to secure a 10am time, it kept pushing us to 1pm. I would go back and the time was still there, but it wouldn't assign that time once I selected my party size. My assumption is that there wasn't enough availability for 6 of us to ride at that time.
This is just my assumption... I'm sure the system is much more complicated