The best time to leave Punta Arenas is early November. The ice will be hard and frozen, the sled sliding over with ease. You will approach the Pole in late summer at -20C, leaving you out of the worst temperature drops of beginning winter.
If you leave later, say the end November, your journey will be a different story. Snowfall and rotting ice will burry your sled and your skis up to your knees. Your sled will feel twice its load. Navigation will be tough in the increasing precipitation of late summer.
You'll approach the pole at altitude in -40C. It's really no fun to travel with the sun declining low on the horizon and freezing temperatures, especially with regards to the South Poles head winds. You fuel will burn out fast and you'll be very prone to frostbite.
Sometimes the flight logistics and ANI financial politics cause delays outside your powers. However, if you can at all - get out as early as possible.