"Until the past few decades, neuroscientists had one way to plumb the human brain: wait for disaster to strike people and, if the victims pulled through, see how their minds worked differently afterward."
"Scientists also discovered that time worked differently for H.M. Up to about 20 seconds, he reckoned time as accurately as any normal person. After that, things veered wildly. Five minutes lasted, subjectively, just 40 seconds for him; one hour lasted three minutes; one day 15 minutes. This implies that the brain uses two different timekeepers — one for the short term and one for everything beyond 20 seconds, with only the latter suffering damage in H.M. Eventually more than one hundred neuroscientists examined H.M., making his probably the most studied mind in history."
The interesting is that the individuals time-perception is disturbed which says that the hippocampus is crucial for time-perception. Declarative memories cannot be formed without a hippocampus, but the procedural memory worked fine. This relates to other things that I have read that says that time-perception is related to episodic memory where time between events are guessed by the brain to know much time elapsed.