One does not warm up a gas turbine - it's not necessary.
Not necessarily. There are airports with extremely low ambient temperatures that when a jet aircraft is parked outside overnight, one has to wait for the oil temperature to reach a minimum temperature after start, as not to exceed the maximum oil pressure allowable for takeoff.
I have also operated at airports that I had to pre-heat jet engines prior to start, as not to risk the starter shafts from breaking*, again only if the aircraft remained outside overnight due to the low ambient temperatures.
* I saw a Lear 24 shear the starter shafts on both engines one morning in Gunnison, Colorado. We tried to tell them, but....