可以加介词的，要看在具体句子里的意思，比如：on that day.在那一天。例句：Suppose flights are fully booked on that day─which other day could we go?
that day例句
1、She never spoke to him again from that day on.
从那天起她就再没和他说话。
2、The memory of that day was indelibly printed on his brain.
那天的记忆永不磨灭地深印在他的脑海里。
3、The article is an accurate reflection of events that day.
这篇文章准确地记录了那天发生的事。
4、He was not in a good mood that day.
他那天心情不好。
5、She gave us her version of what had happened that day.
她从她的角度向我们描述了那天发生的事情。