A few complaints of this nature coming in now the weather is colder. Could simply be that the valve to the heater matrix is not opening fully and admitting heated-up engine coolant to it. May be a sticky engine temp sensor. This is a turbocharged petrol engine with a watercooled turbo that should have the obverse effect of heating the coolant more rapidly. But some engines nowadays are programmed to concentrate heat in the cylinder head and not release it to the heater matrix until the engine is at full operating temperature. If your engine has such a system it could be malfunctioning. I can't see any reason to reject the car at this stage.