Aah - yeah, this part looks fishy, or at least prone to trigger thread+locale-based conflicts:

    if (defined $time) {
        local $ENV{TZ} = 'America/New_York';
        my $est = Time::Piece::localtime()->tzoffset;
        $time = 'Time::Piece'->strptime($time, '%Y-%m-%d %H:%M:%S')
              - $est + $tzoffset;
    } else {
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Manipulating the timezone is weirdly(?) not threadsafe, or at least that's what I remember from some Perl tickets.

Update: You could calculate the timezone once at program startup, that could eliminate the switching of the timezone within a thread.