It wouldn't depend on the guestbook script you are using, if it has a built in feature to set the server time. If not you would either have to edit the script manually, or you can use a line of code in your .htaccess file to set the time zone.

Heres the .htaccess code

SetEnv TZ America/Washington


"America/Washington" is the timezone. As to where to get a list of all the time zone formatting I'm not sure, i'm sure a google search will produce a table with a full list. (Sorry, I don't have a list or a link to a list)

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