Heating - how much time does it take to heat fifth wheel?

I would say a 30 min/1 hr to get the thermostat to desired temps but several hours to rid the unit of cold soak without the heater continuously cycling.
However as others mention one size don't fit all as some units may have a R7 insulating value with a dozen single pane drafty windows vs a unit with 5-6 double pane windows and a polar/arctic pack.

And of course outside temps and wind speed are other players in how fast the heater gets to a certain temp.