Chilli Monster
60 mins is probs a good time, it was decided by someone a while back and gives plenty of time for the 'Plan' to go through the system.. dont forget its not just yours going through, FBUs deal with VFR, and IFR and these all take time..
It is great if you can 'tap into the system' however most people cant do that so play it safe and file at least 60mins before!
SSC.