It's always best to make an appointment just in case it is a day when they are going to be overloaded. However I have never heard of them ever turning anyone away.
I actually went in and did my paperwork 2 days before my drop off to ensure that it was no hassle when I dropped the car off and caught my flight. The day I went in was one day ahead of my reservation. I did email them though and they said come on in.
2014 BMW ///M5 Individual Frozen Grey, Silverstone Full Merino, Piano Black, Exec Pkg, Drivers assistance plus, LED Pkg, Bang and Olufsen, 20" 343M Forged Alloy Wheels
Countermeasures: Bel StiR+, Laser Interceptor Quad HP, Zaon MRX
Upgrades: Eisenmann Sport with M Performance Carbon tips, Dinan anti-roll bars
2015 Jaguar F-Type R Coupe