Can't we use 'in' instead of 'at', if so what is the reason?

[Avi]

English Language Tests, Intermediate level

ESL/EFL Test #203 "Prepositions of Time and Date (1)", question 8

I'm meeting an old friend for lunch ......... noon. I haven't seen her for a long time.

(a) on
(b) in
(c) at

English Language Tests, Intermediate level

ESL/EFL Test #203 "Prepositions of Time and Date (1)", answer 8

I'm meeting an old friend for lunch at noon. I haven't seen her for a long time.

Correct answer: (c) at
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Its quite right to use 'at' for night as well as night.
Cant we use 'in' instead of 'at', if so what is the reason?
Can you please explain the time intervals for morning, afternoon and evenings?

Thank you,

Avi

[Linda]

Hi Avi,
In this case "at noon" or as you added later "at night," the preposition "at" is used because "at' indicates a specific time; whereas, "in" does not.
For example, we can say "in the winter" or "in the evening" because we're talking about a certain time BLOCK or a specific time PERIOD - from beginning to end. But, if we're talking about a specific time - not a time period - then "at" is the correct answer.
You can't say "in noon," "in night" or "in 9:00 pm" when you really mean at that specific time - "at noon," "at night" and "at 9:00 pm."
For most days of the week, we use "on" and for most specific times, we use "at." Sometimes, you could say "at about noon" but again, that indicates a specific time.
I hope that helps.
Linda
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