你理解它的意思,就比较好用了,不要去记它只能跟什么搭配,因为语言是活的,语言是用来表达你的意思的,而不是限制你的
at that time的意思是 在那个时候,请看如下的例子
I was stupid at that time.
I was cleaning my house at that time.
I will be in school at that time.
所以至少我现在想到的这几种时态都可以吧：过去时,过去进行时,将来时