Your trouble can be caused by:
a. Improperly hosting settings (OS, webserver, database, etc.);
b. Improperly Mibew installation or settings;
c. Improperly operation of the browser.
Since you haven't specified any details about your hosting besides the version of PHP, it's impossible to talk about the point a.
Since you have specified correct time settings for Mibew, I doubt that the cause is point b. However, you haven't answered the question whether your Mibew actually works, so it's impossible to exclude the point b.
Since you haven't answered the question whether your Mibew actually works and you haven't wrote that you've got the trouble in several browsers, it's impossible to talk about the point c.
So, for now the only thing that is clear is that something is wrong.