¿Puedo usar "at" y "the" juntos en una oración?
como "at the night" y sino ¿por qué?

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@Guillermo07 You can use “at” and “the” in the same sentence if you are talking about a specific location.
- at the hospital
- at the bank
- at the park
- at the city border
You can also say the phrase “at the time” or “at the moment”
- I was busy at the time
- it happened at the worst time possible
- not at the moment
- I’m busy at the moment

You can’t say “at the night” because “night” is not a location, it’s a thing. You can say “on the night” or “in the night”
- on the night you called, I was too tired to answer.
- it was quiet in the night

Otherwise, if you want to talk about “night” as a point in time, then you just say “at night”
- the party is at night
- I sleep at night
- I usually watch tv at night
It’s similar to these:
- the party is at 8:00
- I sleep at midnight
- I usually watch tv at noon

“Night” is different than “morning” and “afternoon.” You don’t use “at” when talking about something that occurs during the morning and the afternoon.
Instead, you say “in the morning” and “in the afternoon”
- I eat breakfast in the morning
- I’ll call you in the morning
- I have a meeting in the afternoon
- let’s have a picnic in the afternoon

I don’t know why “night” uses “at” but “morning” and “afternoon” use “in the”. That’s just how it works. Think of “night” as a specific time when using “at”, like how 8:00 is a specific time.