When

Not quite. It can be used this way:

Barely an hour had passed when James rang him.

Thanks, MM. But is it okay while using before as in: Barely an hour passed before James rang him.

Yes, that's OK.

Thanks again, MM. Is when okay in these contexts when there's no reference to time?

Example: He was thinking long and hard when the doorbell rang.

A little odd; the 'long' part suggests past perfect.

Thanks again, MM. Am I right in assuming that whenever when comes in the middle of the sentence, the first clause automatically becomes past perfect? Are there exceptions?

Not as simple as that, I think. It is when the order of events is obscured by 'when', since 'when' can mean 'at the same time as an event' and also 'at the conclusion of an event'.