Less and fewer.
Ahem! I think that the wording of the ad is actually correct. Less is for non-discrete amounts: less salt, less water, less courage. Fewer is for discrete items: fewer grains, fewer bottles of water, fewer people.
Measures of distance and time, for example, are arbitrary measures on a scale, not discrete (counted) items. So, I would argue, we would refer to less time, and also time less than a certain measure (whether in days, hours, minutes, &c.) In measuring time, one is not counting discrete lumps or objects, but merely points on a continuous scale.
But I see your point. I will spend the day pondering it (only because I'm working a booth at a show today, and I will be bored).