An SE [day starts at 00:00 UTC](http://meta.stackoverflow.com/questions/27199/when-does-a-day-start).  I am not sure if you, or anyone except diamonds or moderators, can check a user's visitation activity log.  This issue has caused some confusion for [other users as well](http://meta.stackoverflow.com/questions/24884/what-are-the-exact-requirements-for-the-woot-enthusiast-badge/24888).