Could you be specific what changes you are refering is it calender entry, widget time or activate later time or ... ?? Timezone for all server should be same in cluster. Change at system level or pass through system property. Sample below and verify throughly.
 Change the timezone on linux server
Change symlink of /etc/localtime -> /usr/share/zoneinfo/America/Los_Angeles
 Change the timezone is system property
Apolgies for not being clear, we are using Solaris 10 servers in a multi-datacenter environmnet. All of our servers (at the OS level) are set at PST. In CQ, if I make a change to a page and view the modified timestamp - it's showing EST. To be more clear:
Thu Sep 6 15:24:32 PDT 2012
CQ Site Admin Panel's Modified Column
Where is it getting 18:24 from???
We are using 5.5 Update One
When user makes any modification on page the PagePostProcessor saves the content along with modifying date. As it is done at server side it should take server timezone. I have seen issue with earlier jdk bug in one of envirnoment. Coud you please explictely set system property (-Duser.timezone) & verify.