this is the first time this was the first time 怎么用,有什么区别?

貌似这两句短语一样的意思
this is the first time 表示一般句式
this was the first time 表示过去句式
（译作；这就是第一次或时间）
区别；过去式就用this was the first time
一般句式就用this is the first time