"When you pre-book parking in the open surface parking area next to the Terminal Multi Storey car park, as you arrive at the barriers, ensure you drive through the barriers that are 'straight on' (which are labelled as mainly heading for the Covered Multi Storey parking section) - you can still turn left at the far end, to get into the open surface parking area.
If having pre-booked for the open surface area, if you use the two barriers that take you immediately left into the surface car park (as labelled solely for the Surface Car Park), the system does not seem to recognise your number plate and so does not automatically print and produce the car park ticket as you approach - you end up reversing so you can then use the other barriers - assuming that other users do hold back to let you reverse (which many didn't in my case!).
The staff behind Edinburgh Airport Parking are fantastic - if you have a flight delayed, they can be telephoned about the delay and sometimes, they do not always have to charge you the extra time or even extra 24 hours (so always take the number with you on your travels) - it depends which kind individual is on duty.
However, the system will always allow you to arrive 2 hours earlier than your booked time and, brilliantly, let you leave two hours after the original expiry date/time of your ticket, if you have pre-booked.
However, do not chance things by booking less parking time based on this - the prices have already been formulated to allow for the 2 hour entry and exit feature and so you won't save any real money - just potentially inconveniencing yourself should your flight delay is greater than two hours in duration. The parking staff will also know this, since they can look up the flight number time statistics and so they may not be permitted to be as kind as they normally are for those chancing the system!
I'd recommend parking with the Edinburgh airport parking every time you travel from the airport - other providers may not be so accommodating or efficient in delivering you, as the service you can get 24/7 with the official airport parking. When you arrive during the dead of night and all is quiet, you'll be glad you booked the official parking, whatever format of multi-storey, surface, medium or longer term parking you have chosen. Finally, try and book as soon as you can before your trip - the parking charges should be cheaper the earlier you are able to book when compared with leaving it to the week of travelling. "