You'd have to watch it during one of the cycles. Plus, if it has indicator lights, note what comes on and when. A lockout indicates (generally) that the thing tried to fire up, and for some reason, didn't (or didn't think it did). It could be a sticky valve, a bad ignitor, misaligned things, clogged valves, a bad flame dectector, and on some, a bad fan or vacuum switch or partially plugged exhaust or intake. As you can see, there could be lots of things. The theory of operation in the user's manual should give you a good idea of what it has, and some troubleshooting things to look for. If all else fails, maybe a better tech is called for!
The time lockout is for any potentially unburned gas to disipate prior to trying again which will (usually!) prevent things from exploding.
Propane is heavier than air, will pool at the lowest place and potentially accumulate from that low place up. This means that you might not smell it since you're rarely crawling around on the floor. Natural gas is lighter than air, floats up and disperses, so you can generally smell if you have a leak. Both are dangerous if you have a leak, though, and personally, I think propane is worse as it's harder to detect.
