在 (...) 的時候 v. 當 (...) 的時候

[Jose]

Can anyone explain the difference between using 在 or 當 in front of a 的時候 expression?

Thanks in advance

[HashiriKata]

There should be no meaning difference between 在 and 當 in the context you're asking about, the difference is in the structure. 當 always requires a subject to follow but 在 doesn't. Try looking at some examples and you'll see the difference more clearly.