Check the safety switches and that you are in Neutral and PTO Off and these switches are functioning properly. Could be Switch, Wiring or Starter Switch or even starter or starter solenoid causing concern.
You want to be careful doing that and running high rpms when engine is cold. Best method is use the Glow Plugs and if that cold and you need to start add a Coolant Heater option. High RPM and Cold Engine can accelerate wear and damage the engine causing premature failure.
Depends on air temperature. In Warm weather a few seconds in cold weather it will take longer. Try starting if it spits and sputters increase glow plug time.
