OK, I thought we were talking theory here, not reality. There is a big difference. In theory, your husband is right, not sure I would want to be in the car with him though if he follows this in practice.
If you want numbers, in my experience it takes a car about 5-7 minutes to reach operating temperature when the outside temperature is around freezing (32F). Operating temperature is when the coolant reaches the temperature when the engine goes into closed loop. Closed loop is the term used when the computer uses only its sensors to control the engine and stops running in a preprogrammed mode to compensate for a cold engine. The coolant temperature on most cars for that is around 180F.
From the moment the engine is started, it begins to heat up and the coolant in the block begins to heat up also. The water pump starts circulating the coolant, but because the thermostat is closed, the only circulation is through the heater core. It may take 15-20 seconds before the first ever so slightly warmed up coolant reaches the heater core and can be transfered to the cabin. If the blend doors or the coolant valve is wide open, then that little bit of heat is available.
While in theory, the say 33 or 34F air is warmer than the 32F air in the cabin at start, and it is providing warmth, I’m personally not fond of blowing 34F air on my legs at the maximum wind speed the fan is capable of. I’d much rather have 32F still air on my legs than fast moving 34F air, something to do with wind chill makes it uncomfortable.
In some cars, the temperature gauge shows cold until the thermostat starts to open. I know on our Honda, the gauge stays at the lowest position for about 4-5 minutes, then rises to normal in the space of about 15 seconds. Not all cars do that but some do. But most of them will not start moving the needle until the engine coolant is up to around 100F + so even though the gauge might be on zero a minute after starting, the coolant may now be warm enough to turn the fan on and start heating the cabin up.
For practical purposes, you are looking at a coolant temp rise of about 30F per minute. You really don’t want moving air across your skin that is less than 70F, so if the outside temp is 32F, you need to wait about a minute and 20 seconds plus teh 15 to 20 second delay to get from the engine to the heater core, so a total of about a minute and 40 seconds before turning on the fan, and then you might just use low until the coolant temp rises another 20F or so before going to a higher speed.
Now about your theory, the sooner you open the valve or blend door and turn on the fan, the sooner you start heating the cabin, but the rate of rise in the temperature of the cabin will be very slow at first, but rise to the maximum rate of rise as the engine heats up. If you wait until the engine is fully warmed up, then turn everything on high, you get the maximum rate of rise right away, but you sat in a cold cabin for 5 to 7 minutes when you could have been getting some warmth 3 to 5 minutes earlier.
In other words, you could sit in a cold cabin for 5-7 minutes, then turn every thing on and be warm 3 minutes later, or you could have suffered for 2 minutes, then gradually got relief and could be in a comfortable cabin before the engine reaches operating temperature.