I'm just using the SUNRISELOCAL$ and SUNSETLOCAL$ WC tags in an html page that is parsed by the app every 2 minutes. For example:
<?php echo "<td class='left'>".strtolower('SUNSETLOCAL$'); ?>
PHP on the server then formats it as I want.
Only thing I can suggest is to be sure your computer is updating the time properly. System Prefs/Dat & Time->Date & Time
tab:"Set date and time automatically:".
Perhaps also double-check your Lat-Long location. I don't see any place to set the offset from UTC in WC.