GMATPREP question need help

[Sage Pearce-Higgins]

No need to repost my post in your reply.

Here are my answers:
I slept less than 6 hours last night.Correct. Since we measure time as a continuum, we're talking uncountable here. If you use 'fewer' it sounds like people only sleep in whole numbers of hours and never something like 6.5 hours.
Last month I worked 5 hours of overtime, but this month it will be 2 hours less. Correct for the same reason.
The amount of hours that we spent on this project is incredible. Incorrect. Even though we might not have spent a whole number of hours on the project, the phrase 'amount of [plural noun]' is incorrect.
How much do you sleep at night?

Correct

Stacey ran a marathon in fewer than 4 hours. Incorrect, for the same reason as the first one.

[nahid078]

Why "less than 35" rather "In less than 35"

The big idea here is that if a time interval is unmodified, then we typically use "in" or "for." Notice, that the modifiers such as "more than" or "less than" don't change the basic pattern.
In three days, I will do X
In less than two years, I will do X.
For more than six years, I did X.
BUT, and this is very important, when the time interval is modified, by a preposition or a clause, we do NOT need a preposition.
Three days after the wedding, I did X. = preposition modifier
More than six years before the French Revolution, he did X. = preposition modifier
Less than five minutes after you called, I did X. = clause modifier
Two days before you returned to town, I did X. = clause modifier

In this sentence, the time interval "three years" is modified by a clause beginning with a subordinate conjunction ("after" in (A) and "since" in (C)). Because it's modified in this way, it does not need a preposition.

- Copied from a post by mikemcgarry

[Whit Garner]

Why "less than 35" rather "In less than 35"

I will completely agree that technical grammar rules can be awesome - that said, for the GMAT, I find that working to understand the why behind the meaning rather than just the grammar rule can be more helpful. When you're dealing with a vast universe of grammar rules, trying to memorize every single nuance and then recall it during a timed exam (in under 2 minutes) is too much. I'll tell you that the vast majority of native speakers won't have any clue about the rule listed above - I certainly haven't ever used it before.

Also, I'm not clear what is meant by unmodified vs modified in the explanation posted, because in every example above the time is modified by a preposition. I think what the original poster might have meant was that they didn't need multiple prepositional modifiers, but I think the explanation is oversimplified or maybe overcomplicated - I honestly can't tell which.

The fact is that any of the following would likely be okay:

"In less than 35 years after..."
"Less than 35 years after..."
"In less than 35 years since..."
"Less than 35 years since..."
"In the 35 years since..."
"In the 35 years after..."

It would be extremely unlikely that the test would make you decide on something this nuanced and stylistic. Again, I'm not sold that there is actually a rule out there for this that everyone would agree with.

I hope this helps anyone who wants some additional clarity on that possible grammar "rule."