Please tell me during the 5 days is not okay?
안에 to me sounds like inside of, so I think of it as tell me within 5 days whether it be the 5th day or first.. "In 5 days" sounds like exactly on the 5th day.
How is that not right?
During 5 days sounds unnatural to me. If I want some info within a period of time, I'd ask just like this.