I sent the package first class on Monday.
我于星期一以最快投递邮件寄出包裹。
On Monday he would have to return to his regular duties.
星期一，他就得回去正常上班了。
They arrived on Monday evening and we got there the following day.
他们是星期一晚上到的，我们次日也抵达那里。
Please note the office will be closed on Monday.
请注意办事处星期一将关闭。
The school will be closed Monday because it's a holiday.
星期一是公共假日，所以学校不上课。