Don't worry about checking in your entire party. As long as one of you has an early time, you can all check in at that time. I can't remember exactly where it is written but, somewhere in the fine print it says to arrive with your entire party at the scheduled time. As long as one of you has an early time, your entire party can arrive at that time.
All this arrival time stuff may be moot anyway. They aren't enforcing it at many departure ports.