This script returns a Boolean logical "true" if DST is in effect and a Boolean logical "false" if not. This is valid for the "new DST schedule" 2007 and up DST times in the US. Those countries and areas beginning and ending at different times may have to adapt slightly.
DST Boolean Quick Test
This routine to determine DST tests for the potential of DST by checking a time of the year that is typically in DST and another that is not. If the date you run this script falls between, a logical "true" is returned indicating that DST is in effect. The test in bold is the output of the script. View the source...