Works really fast Kungfucheez, after setting up an account at PayPal you can use it right away. PayPal works fast, my payment at JoyGP was taken care of instantly, I only had to wait until daytime in Korea (for them it was the middle of the night).
It works like this: you buy mileages at JoyGP, pay for them with PayPal (at the JoyGP site, it's easy), after confirmation from PayPal JoyGP adds the mileages to your account and with these mileages you 'pay' for your games.