in 5 minutes有连个意思.
一.表示在5分钟之后,表示将来的概念.如：he' ll come to see you in 5 minutes.
二.表示在5分钟之内.yesterday i finished my work in 5 minutes.
after 5 minutes表示过去的概念,在过去某个时间的5分钟之后.
如：at first he said he would do it at once ,but after 5 minutes,he went out and forgot what he had said.