I can only speak from my Tesla experience. The car takes no longer to heat/cool than an ICE car, and has the bonus that as long as the car is plugged in then pre-heating doesn't use any battery energy. Hetting into a defrosted car with the interior at 20C is a nice experience.
The latest Tesla cars have an air source heat pump/air conditioning unit that is part of a complex liquid based heating and ventilation system.
The fluid is connected to the cabin heater, engine CPU display and main car computer and the battery. A sophisticated CPU moves heat energy from where it isn't needed to where it is, for example on a cold day a car parked in the sun will harvest heat in the cabin and the car will use some of this to preheat the battery, for greater efficiency.
In winter the range of the car falls, by about 20%, but this is down to a number of factors.
I feel that any conversion of a classic to an EV is bound to compromise heating and ventilation and eat range.
