It'll turn over at the exact time you joined iirc
I mean like the exact hour you joined, so if you joined at 9pm, it'll be available and switch over to 10 years at 9pm
I'm not 100% sure but iirc the number of months that it counts are strictly 30-day months, which is not always accurate obviously. More importantly, 4 weeks don't always equal one month. But your join date is on your profile as December 16th, so it's not off by two days. It's just a matter of waiting until the exact time of the day you joined.
Four weeks = 28 days, plus the two extra days make it 30
The join date on your profile is the 16th though which is today, and that's the date to really look at. If you don't get the loyalty box by midnight (remember go to the user dashboard first to get it), file a ticket, but for now, it's probably just a wait until the exact minute you joined 10 years ago :)