有两种用法。
1. It's time to do。该去...了
2. It's time sb did。某人该去...了
对第二种用法举个例子
It's time you went to bed. You'll have to get up early tomorrow.
你该去睡觉了。你明天要早起。
相当于 You should have gone to bed now.
你现在应该去睡觉了。
这里的虚拟就是指 你应该去睡觉了,但实际上你现在还没有睡觉。
同样
It's time we went home. 我们该回家了(实际上我们还没有回家)
It's time they went there. 他们该到了(实际上他们还没到)