It's not the first time that/when you've found yourself in this situation.

[diamondcutter]

It's not the first time that you've found yourself in this situation.

Source: Collins COBUILD Advanced Learner’s English Dictionary

Could we use “when” to replace the conjunction “that” in the sentence above?

 

[Tarheel]

In my humble opinion, no.

 

[diamondcutter]

It’s the first English book that/which I’ve ever read.
(By me.)

What about this sentence? Have I used the conjunction (that or which) correctly?

 

[Tarheel]

You can use either one. However, nothing is needed there. Say:

It's the first English book I've ever read.

 

[jutfrank]

Could we use “when” to replace the conjunction “that” in the sentence above?

No. Use that after superlatives and ordinal numbers.

It’s the first English book that/which I’ve ever read.
(By me.)

What about this sentence? Have I used the conjunction (that or which) correctly?

Use that. Or, as Tarheel says, nothing at all. Don't use which.

 

[diamondcutter]

Could I ask which pattern is more common, using "that" or "nothing at all"?

 

[5jj]

Probably nothing.