There's no need to reinvent any part of this wheel. Time::Piece:

use Time::Piece;

my $str = '2005-03-28 12:00:00';
my $fmt = '%Y-%m-%d %H:%M:%S';
print Time::Piece->strptime($str,$fmt)->epoch;

__END__
1112011200
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There are many other handy shortcut methods as well...

hth