If you know the difference between less and fewer, you already know the answer: it all boils down to non-count nouns and count nouns.
In other words: Are you referring to stuff of a general quantity or to something you can actually count, such as on your fingers?
A NON-COUNT NOUN: TIME
You can't count time. It's a general noun. You can say you spent a lot of time or a little time on something, but you can't count time.
COUNT NOUNS RELATING TO TIME:
You can, however, break time into countable pieces like hours, minutes, and seconds.
So I spent three hours on a homework assignment. I watched television for thirty minutes. I ran that lap in sixty seconds. Those are all count nouns.
In the same way, you can't count flour (it's a general thing, a non-count noun), but you can count things you break the flour into: bags of flour, cups of flour, spoonfuls of flour (bags, cups, and spoonfuls are all count nouns).
Bringing it all back to MUCH and MANY:
If you're referring to a general amount of "stuff," a non-count noun, use MUCH:
I don't have MUCH money.
(Money is a non-count noun. You count money by breaking it into dollars and cents, which are count nouns.)
How MUCH food did you eat today?
(You can't count food, but you can count French fries, slices of pizza, or apples.)
On the other hand, if you are using stuff that can be counted, than you use MANY:
I don't have MANY dollar bills in my wallet.
How MANY crackers did you eat?
And the same rules apply to LESS and FEWER.
LESS = NON-COUNT NOUN (So: LESS flavorful, LESS healthy.)
FEWER = COUNT NOUN (So: FEWER trips to the store, FEWER split ends.)
But apparently, the people who make commercials don't know that, as we're constantly being told that products have LESS CALORIES and channels have LESS COMMERCIALS.
(Fewer, people! Fewer!)
And yes, every time I hear those things, I do twitch. In case you were wondering.