Consider the following sentence:
One disadvantage of exams is that students feel really irritated if they mess up one.
Is it correct if I change it to this one?
One disadvantage of exams is that when students mess up one they feel really irritated.
Is it correct and natural to use "that when" in this sentence? I've read in a grammar book that using two relative pronouns is incorrect, but here they do not refer to the same thing.