If you were talking about time... you would say I'll meet you AT 5 o'clock but you could also say I'll meet you IN a few hours The difference is that you would use AT when you're going to say an exact time (5 oclock) or an exact place (home, school, the shopping mall etc). You'd use IN to say an AMOUNT of something or when you actually will be physically inside something (in 5 minutes, in a whlie, in the parking lot etc). It can be tricky in some cases because you can meet AT the shopping mall or IN the shopping mall (both are good english). You would pick AT if you had an exact place in mind (at the mall entrace). Some native speakers mix them up too so don't feel bad you'll be understood either way. Hope that helps. Alex