I'm not sure if this is the approved method, but I needed to change my time zone settings after we switched to Daylight Saving Time. I just went into the file hesk_settings.inc.php and searched for diff_hours. That gives you a number that the tickets are offset from the server time.
My server is on GMT, so my change was from -6 to -5 to move from CST to CDT. YMMV.
(Yes, this is an old ticket, but it wasn't answered and came up when I was searching for this answer.)