one of the documented procedures in this installation of the ACS
What it does:
Looks at ad.ini file to see where server is located and also at last element of ns_localtime to see whether we're on daylight savings time or not
Defined in: /web/philip/tcl/ad-last-visit.tcl

Source code:

    # [lindex [ns_localtime] 8] will be 1 if we're on daylight time, 
    # 0 otherwise
    set daylight_adjustment [lindex [ns_localtime] 8]
    return [expr [ad_parameter HoursDifferenceFromGMT] + $daylight_adjustment]