Deo,
It should start without the grids... I never wait for mine until the temps are in the mid 30s. I just crank and go. Usually starts on the first compression stroke.
Maybe your battery is on the way out... a diesel needs to spin fast to start.
That happened to me one morning last fall... . was turning too slow to start. Battery load tested marginally good, but didn't have enough to start the engine.
Later that day... new battery and problem solved.