2001 Chevy Silverado my car wont start when I need it to.

Next time it won't start, don't wait.
Do below:

Get a helper disconnect a sparkplug wire or 2 and ground it to the engine -have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel related problem, check the fuel pressure to rule out the fuel filter/fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light. No snapping blue spark continue to troubleshoot the ignition system-power input to the coil/coil packs, coil's resistances, distributor pick-up coil, ignition control module, cam and crank sensors and computer Note: If it doesn't apply disregard.
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I had a problem similar to that on a GM car I had. When the engine was cold, it would start and run for days if needed. But if I shut it off and tried to restart it when the engine was warm, it would not start. The problem was the CKS (Crankshaft Position Sensor). Solved my problem.