I also dont know the motor.
There are glow plugs with elements that burn an element red hot and what I call heaters which are an encased element.
With encased element type I give them 8 seconds ,turn them off and crank the engine.
Mine are drawing 60 Amps on a 3 cylinder VM motor and the starter draws 80 Amps so its one or the other and I think this is common with diesels
Now I had the case that the engine did not start. I kept cranking and cranking and perhaps if the battery held out it might start. Throttle was tried at many start positions.
Once hot it started first time every time .
Solution- After pulling the engine and fuel distributor to pieces and checking everything it was as simple as replacing the needles and nozzles on the injectors. The fuel was dribbling in instead of spraying in.