说反了。先行词被序数词修饰都用that ，比如 It's the third time that you've arrived late this month. 

只用who 不用that的情况：

1.关系代词在介词后面，比如 I sent thank-you notes to the relatives from which I received gifts.

2. 非限制性定语从句， 比如 He lives in a big house, which has a garden.

只用that不用who的情况：

1.先行词是 anything, something, nothing,everything等不定代词，比如 He never reads anything that is worth reading.

2.先行词是 all,much,little,none 或 被这些词修饰时，比如 You can take any seat that is free.

3.先行词被最高级，序数词修饰，或被 the first, very, the only, the same 修饰时，比如My book is not the only thing that is missing.