While searching for a quote about Pon Farr at Star Trek Script Search, I came across this exchange from the VOY episode "Flashback":
We know from TMP that Spock spent no more than two and half years studying Kolinahr and was ready to achieve it when V'Ger came along.
So why did Tuvok study for six years while Spock completed his studies in two and half? Does everyone proceed through Kolinahr studies at their own pace? Did the studies become more complex between the times that Spock and Tuvok began them? Is Tuvok just a slow study? Did VOY ever go into more detail about this?
TUVOK: I returned to Vulcan, where I spent several years in seclusion, immersing myself in the Kolinahr, a rigorous discipline intended to purge all emotions. I wanted to attain a state of pure and total logic.
JANEWAY: What happened?
TUVOK: Unfortunately, six years into my studies, I began the Pon farr. I took a mate.
We know from TMP that Spock spent no more than two and half years studying Kolinahr and was ready to achieve it when V'Ger came along.
So why did Tuvok study for six years while Spock completed his studies in two and half? Does everyone proceed through Kolinahr studies at their own pace? Did the studies become more complex between the times that Spock and Tuvok began them? Is Tuvok just a slow study? Did VOY ever go into more detail about this?