Ok this is what i had in mind, i create an event from A to B on the specified date and time, this then is visible on a page for pilots to see url could easily be published in forums / frontpage news.
On the page will be listed event from and to with a banner and date / times for booking a slot flight plan details or any other text.
Variables to be used would be Depart icao, Arrive icao, Date and time span.
Along comes a pilot and they want to fly in the event so maybe from a dropdown menu they can select departure time (times would be read from the created timespan with a 5 minute slot) and departure icao (this would populate from the depart or arrival set when the event was created by admin) input callsign and submit, this would then show an overview of what they have just booked and all other bookings that have been submitted for the event.
I hope i have explained it ok,