@ahmedmoz,
He played a trick on me on April Fools Day. [right]
He played a trick on me in April Fools Day.
I'll help you in a minute. [right]
I'll help you at a minute.
I'll be ready in a few minutes. [right]
I'll be ready at a few minutes.
I have a flat on the second floor. [right]
I have a flat at the second floor.
I'll meet you in the morning. [right]
I'll meet you at the morning.
I'll go to the restaurant with you in the evening. [right]
I'll go to the restaurant with you at the evening.
The sentences not marked "[right]" are definitely wrong.