The definition of adverse driving conditions in the regulations means snow, sleet, fog or other adverse weather or road conditions that were not known to a driver or a motor carrier dispatching a driver immediately before the driver began driving or could not reasonably be known to them.
That is the definition in the regulations, so that's the core of how section 76 needs to be interpreted with respect to the guidance.
I would also note from a regulatory perspective that within the regulations there are limits on driving time as well as on duty time. The driving time is 13 hours, and two hours can be added in adverse conditions. For off-duty time, you can also defer two hours of off-duty time, so that accounts for things like loading and unloading where you would not be driving but you would be on duty.