for s in server ; do
from_date="12-Jan-2015 12:02:09"                        # works in same shell
to_date="24-Jan-2015 13:02:09"                          # same
ssh -T $s <<-EOF
$(echo $from_date)                                      # same as just $from_date 
$(echo $to_date)                                        # same
$(epoch_from_date=\"`date +%s -d "$from_date"`\")       # works, but in sub shell
$(epoch_to_date=\"`date +%s -d "$to_date"`\")           # same
$(echo $epoch_from_date)                                # var is gone with sub shell
$(echo $epoch_to_date)                                  # same
EOF
done