$ENV{TZ}="US/Eastern";
# use locatime(time) to get the time
$ENV{TZ}="Other/Zone";
# use localtime(time) to get the time
# subtract the difference

##</code><code>##

my $rfc_offset = `TZ=US/Eastern; date +%s`;
my $rfc_offset2= `TZ=Other/Zone; date +%s`;
# code to work out difference in seconds.