Vulcans mate normally any time they want to. However, every seven years you do the ritual, the ceremony, the whole thing. The biological urge. You must, but any other time is any other emotion—humanoid emotion—when you're in love. When you want to, you know when the urge is there, you do it. This every-seven-years business was taken too literally by too many people who don't stop and understand. We didn't mean it only every seven years. I mean, every seven years would be a little bad, and it would not explain the Vulcans of many different ages which are not seven years apart.