Board Thread:Support Requests - Getting Started/@comment-27242792-20130910013826/@comment-188432-20130910110239

You can't game the system by changing your computer's time zone, or your account's timezone. Achievements are based on UTC for reasons of fairness. A day is 0000 to 2359 UTC as measured by Wikia's servers. Period. No trickity tricking that. A day must be precisely 24 hours, as reckoned by a neutral observer, for the badge to have any validity whatsoever.

A good way to help you not lose track of time is to install a UTC clock on your wiki. Or you could just remember to make one edit at the same time in your local time zone every day. See Admin Central:Guide to Achievements for more.