A DD 6V92 should start instantly. Much quicker than the usual 4-stroke engine.
It takes 3 things for a diesel to run:
1. Air & lots of it.
2. Clean fuel
Since it's unlikely that you've lost compression because that requires a mechanical failure, that leaves air & fuel. In most diesels, the most common issue is fuel but DD's can also have issues with air because of the air flapper under the blower. Since it's easy, I'd check the flapper and make sure it hasn't been tripped.
Next, check for fuel. Does your installation have a fuel cutoff solenoid? I'd expect not since it's DDEC, but someone may have spec'd it that way out of force of habit.
If that's OK, then I'd check out the DDEC system. As I recall, the timing sensor is a likely culprit. Check for loose or disconnected wires at every sensor on the engine.
Steve & C. J.
2009 Arctic Fox 29V PullRite 20K hitch
2005 Chevy Silverado 2500HD 4X4 Duramax/Allison