Here’s how to determine the dates when the Daylight Savings Time changes for a given year (I keep forgetting how to do this.):

zdump -v /etc/localtime|grep 2008

/etc/localtime  Sun Mar  9 06:59:59 2008 UTC =
    Sun Mar 9 01:59:59 2008 EST isdst=0 gmtoff=-18000
/etc/localtime  Sun Mar  9 07:00:00 2008 UTC =
    Sun Mar 9 03:00:00 2008 EDT isdst=1 gmtoff=-14400
/etc/localtime  Sun Nov  2 05:59:59 2008 UTC =
    Sun Nov 2 01:59:59 2008 EDT isdst=1 gmtoff=-14400
/etc/localtime  Sun Nov  2 06:00:00 2008 UTC =
    Sun Nov 2 01:00:00 2008 EST isdst=0 gmtoff=-18000

Obviously, change 2008 to whatever year you want.