I was really excited as yesterday was apparently my Subeta birthday and Loyalty Box! However, for some reason site preferences won't say six years, only that I've been a member for "5 years, 11 months, 4 weeks, 1 day". Which, if I'm not mistaken, is 6 years?

... I guess it's not so important, but I'm just really dying for that Loyalty Box. XD

Nope, you're one day short.

Check the DATE you registered, because it's what matters.

Yup it is based on the day you registered , not that wonky timer xD Make sure you visit your user prefs page when it is time and that activates it.