on time 含义是“在正点的时候”，即按时、准时、正点，如：
The car was not returned on time. 这辆车没有按时归还。
For once you leave bang on time for work. 你终于有一次准点上班去了。
Don't worry, she'll be on time. 别急，她会准时到的。
in time 含义是“在规定时间内”，即及时，迟早，如：
I arrived just in time for my flight to London. 我及时赶上了飞往伦敦的航班。
The doctor came in time to save his life. 医生及时来抢救他的生命。
In time you'll forget him. 你迟早会忘了他的。
