Just a few tips from a non-expert.

It should only take a few seconds to ramp up. Too much air or not enough propane will keep the temps down below ramp temp. Give it more propane or pulse/blip the starter to keep the speed lower to let the temp come up without flames out the back (it's a balancing act). Once it starts to ramp on kero, keep the starter fully engaged till about 28,000 which will come quickly. Turn off the glow plug and propane any time after it is ramping well. The exact time isn't critical. After shutdown cooling air in the intake is good or use the starter to cool it down to about 110 C.
Also make sure the thermocouple is the proper depth into the exhaust cone.

Why did it only run for ten seconds? It takes longer than that to spool up to idle. What was the RPM?

Sara from Wren will answer any questions you have. She is the expert.