After our recent rewatches of TOS, I came away from Amok Time thinking Pon Farr really only happens to male Vulcans and only once in their lives around the age of 30.
I think that was Sturgeon's intention: Ponn farr is one-and-done. You go home and get married. But then came "The Cloud Minders" in which Spock clearly says Vulcans go into heat once every seven years.
My theory: when they wrote "The Cloud Minders" in the age of paper-only documents, it was too much trouble to find a copy of "Amok Time," so they went from memory. Spock said his marriage to T'Pring was arranged at age seven, and he mentioned some giant eel birds that must return to their hatchery every eleven years to mate. This got mixed up in the writers' minds and came out "Spock has to mate once every seven years." So a false memory became canon.