in：过……后（未来时间）注意如果用于过去时,用after +时间、She went to Nanjing last May,and she came back after a month、去年五月她去了南京,一个月之后她又回来了、大多用在将来时（一般将来时和过去将来时）、in an hour 一小时之后in a week or so 一个多星期之后He will be back in five hours、他五小时之后回来、
They said they would arrive here in a week、他们说他们一周后到达、
within：不超过……的范围比较within和in with in强调在……时间之内,没有时态的限制、in是以现在为基准,in an hour是指从现在起1小时之后,所以一般只用于将来时、within 3 hours 3小时之内I must finish painting the cat within five minutes、我必须在五分钟之内画好这只猫、They worked hard、They finished the workwithin 2 days at last、他们努力工作,结果终于他们在两天之内完成了这项工作、