general time question

Hello again; I am developing an application that uses php with Apache. A user requests a script file from a web site and the server takes such things as $_SERVER['REMOTE_ADDRESS'] and uses php's time() function to record the time in utc code (which would be the server's system time) and other bits of info and saves it in a php script file on the server. The script is a login script. When the user successfully logs in. Javascript is used to send the client time and time zone offset. These are written to this file also. To track the user for statistical and authorization reasons this file is used to authenticate each user request and track usage. What I do not understand perfectly at the moment, and I have to learn somewhere sometime, is the figures that are recorded. I know, I could use php's built in session handling but I have special reasons for doing it this way. These are the values I am recording: (a sample php script file) $sid = '96f120f9dcf293e64e6dcbd16024491e'; // this is a session id

$da = '1200867964';                                          // this is the value generated by the time() function

$hid = '2c9a46c1a5d89469481951065cc6a621';// another session id

$ctzo = '480';                                                      // This is time zone offset according to what javascript sends
$ctzn = '1200868142247';                                  // This is the client time according to javascript, which is supposed
                                                                           // to be in milliseconds

The specific questions are what does the offset '480' mean? (add or subtract from utc/GMT to get local time?) I am in Pacific Standard Time testing this script. The server is also at the same location. The javascript time value should be the original request time plus the time it takes for a successful login to be processed: The user types in the info and clicks the form button the client pre submission script is run then the server receives and processes $_POST values and decides if the user has sent a valid id. Javascript time value is specified as milliseconds. millisecond is 1/1000 of a second, right? and dividing the value by 1000 would give seconds elapsed from Jan 1 1970(?) thank you in advance; Jeff k