Could be the cold, could be something not related to cold. Which means a long list and tests. Google it or give us all the info and history. If you are sure it's cold weather, get a block heater. It's just Mother Nature thickening the oil and shrinking all the moving parts and messing with the battery, thus: slow starter. But we don't know your info, history and manifestation of "hard to start".
This will do the trick.
Many folks don't drive their vintage trucks in the winter.....salt!....slippery!......no ABS.....hard start.....no heater!!!!!!!!!