Please help about last modified date and time

While setting the server timezone as described here should fix the problem, one thing to note is:
while Plone has timezone support for event content objects, there is no timezone support for the created, modified, effective and expire dates.
We need timezone support for those dates also and it wouldn't be too hard to add such support, but it just didn't happen yet.
Also see: https://github.com/plone/Products.CMFPlone/issues/1298

My solution is a patch, like said below Plone should have proper support for timezones. Until this is done and you can upgrade Plone, any re-installation will remove the fixes. Also if you look at other parts of Plone like searches, comments, the date timezone settings are not fixed. This is very much a temporary workaround, nothing more.

Hi Mikel,

I tried following your instructions (3 different ways) and added:

[instnace]
environment-vars = TZ America/Los_Angeles

  1. tried adding the above to the zope.conf. identical results.

  2. tried adding: zope-conf-additional = TZ America/Los_Angeles
    (try #3, comes from http://www.teamrubber.com/blog/oddness-changing-time-zone-in-zope/)

after each change, I ran buildout and got this: "unused options for buildout: environment-var"

site ran fine, but no change to TZ.

I'm running Plone 508

any help would be appreciated

That error means that you are not putting the environment-vars (note the plural) option in the correct place.

It must go under the section that creates the Plone instance, which usually is [instance] but may be another thing.