1. It's time that 这个句式中的 that 常可省略。如：

It's time I fed the dog. 我该喂狗了。《朗文当代英语词典》

It's time we were going. 我们现在该走了。《牛津高阶英汉双解词典》

2. 费致德《现代英语惯用法词典》（P.503）有如下介绍：

It is time 后面用虚拟语气过去式。口语中常用。

It is (high) time you went (were going; should / had better / had rather go).该你走的时候了。

It is high time that you should go. 是正式文体。were 有时也用 was。