This/It is the first/second … (序数词) time + that 从句 属于什么从句?

This/It is the first/second … (序数词) time + that 从句 属于什么从句?
1 This / It is the third time that you have been late this month
请问：This/It is the first/second … (序数词) time + that 从句 属于什么从句?
这类句型 that 后面属于什么从句,网上看到有各种说法.
定语从句,主语从句,同位语从句,强调句,固定句型,
我觉得,定语从句可以排除吧,比如例句中 third time ,在从句中不做成分哦.
强调句,貌似 去掉 it it that 后,the third time you have been late this month
You have been late the third time this month
感觉句子也有问题啊,句子不通顺哦
请分析,适当讲解
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2 You have been late the third time this month
语法是否有错误 请 说出来 .我的理解是?是不是 第三次 不能从过去,延续到现在吧?
You have been late three times this month 这个就没问题了吧.
3 the second ,the first time 前面是否可以加上介词,比如 for
last time 前面就不用加介词了吧?
请按顺序 回答.
前辈,我在百度和谷歌,有些网站查到,这么说的.
It/This is + the + 序数词+ 时间+ 定语从句(从句用完成时).
有些 英语学习网站 分析说这句是定语从句,但是觉得定语从句,first time 也不在从句中做 成分合适么.,我觉得定语从句不对.呵呵
This / It is the third time that you have been late this month
我也觉得 是同位语从句,有人说是 主语从句?有何不同么.