From what I would consider fairly extensive experience in winter operations 20+ years here in Canada where winter ranges anywhere from a few weeks to 5 months each year. Here is my take and our company SOP.
The holdover tables contain a range of times in each cell for each temperature and precip condition, the lower of these times is the no inspection required holdover time. Provided you do not exceed this time you may depart with no further action required by the crew. If you exceed this lower time in the cell but not the upper limit, a visual inspection of a representative surface on your aircraft (usually the upper surface of the wing visible from the cabin) is required and must be free of contamination before a takeoff is attempted. If the upper time in the cell is exceeded the aircraft must return for additional deicing and/or anti-icing.
Hope that helps.
Dave