This script demonstrated on this page will produce a perpetual SMART BUSINESS HOURS CALENDAR.  It incorporates the ability to adjust for daylight savings time or standard time notations (the USA version) and automatically generates U.S. national holidays (plus Easter). The script allows you to program business hours for each day. It also allows you to override the automatically generated schedule with whatever you like - vacation days, for example - and you can add information/links to your schedule for a given day (i.e for sales and promotions).  To use the script, view source, copy to the desired location and edit it.  Be sure to read all the instructions to use the full functionality of the script.