I would recommend that you install the php intl package and see if it resolves your issues.
You should also make sure that all your timezones match. In PHP (php.ini), MySQL (my.cnf or my.ini [see query below to see settings]), server OS, profile, osTicket Admin panel -> Settings -> Default Time Zone.
This SQL query can be used to see your time_zones in MySQL:
SELECT now(), @@GLOBAL.time_zone, @@SESSION.time_zone;