My Gravograph LS900, from the moment the screen shows it's loading data (via parallel port), I can start lasering. Actually, all of my Gravo/New Hermes equipment will run before the job data is fully uploaded.
My Triumph and GCC won't show a new job until it's fully loaded up.
All depends on the maker I suppose, and it seems the GF lets you run while uploading. Even though the machine instruction data is digital, it's loaded and used analogously, shouldn't be a problem. It's not with my machines...