based on its better to be early than late...
I guess we need to check in around 1:00.
Yes it may take us 2 hours to get to the car parking but it could also take 3 1/2 hours.... The M62 did this recently to me when I had to get to Liverpool for 11:00 am, I left York at 8:15 am and made it with 3 minutes to spare !!!!!
The car parking is 15-20 minutes away from the airport, so if we arrive at the parking by 12, transfer bags, faf about, drive to the airport, check in, try and get through security with all the climbing stuff, I would say it is the time to try and set off.
Cefyn