Explanation

You can see the doctor at 8:00 a.m. and 12 noon

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the preposition “at” can be used such as telling time or location (e.g., telling someone to meet “at midnight” or “at the coffee shop”). 

In the above sentence, we use the "at" preposition because " someone meets the doctor at 8 a.m. and 12 noon"

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ND10-1-2023