I thought I missed a day, but looking at it, this looks really weird: http://area51.stackexchange.com/users/66506/
It says 8 consecutive days, but visited 10 days in total. That would require at least 11 days of history right? But it says member for 10 days only. Note: Figures may change over time.
member for 10 days visited 10 days, 8 consecutive seen 3 mins ago
It can be determined that the method for counting the member for days is implemented differently on area51, and other stackexchange accounts (including stackoverflow, meta, ...).
Generally, the member for count is equal to the number of UTC days you have been registered for (including partial days).
However, on area51, member for is equal to the actual time you have been registered for (in days), rounded down.
Thus, before my registration on area51 at UTC 01:01:53 (currently UTC 00:58), it will say:
member for 10 days visited 11 days, 9 consecutive seen 6 secs ago
This inconsistent behaviour should be fixed.