You make reservations for other members the same way you make reservations for yourself. Because you are an administrator, when you click on the calendar to scheduler a slot you will see a dropdown with the other members of the boat - as long as they have available slots you can choose their name from the drop down and book the slot for them.
We are working on being able to bring unused slots forward and taking slots from the next month - it turns out to be fairly complicated given the way we build the calendar, so it may take us a little time but we will be able to do it. I will let you know once we get it completed.
Regarding the nighttime period, you will notice that the time period for your slots as you have your calendar configured is 10am to 10pm and 10pm to 10am. To book the nighttime slot, you would need to book both slots on a given day by clicking on each slot and booking it for the appropriate member. You could also configure your calendar to have just one slot per day which would allow you to book an entire 24 hour period with a single booking - please not that if you change the number of slots per day, it will delete all future bookings for you and your members - they will receive an email and can re-book the slots however.
We do have the functionality that allows for bookings within 24 hours not to count against your total time, but it has been disabled for some reason. I will check with the developers and see what is going on with that and let you know.
I'll be back in touch as soon as I have some information for you - in the meantime don't hesitate to contact me with any other questions or clarification about the above.