use strict;
use constant HOUR=>  3600;
use constant DAY => 24* HOUR;

sub RunAtTime {
 my $RunAt = shift * HOUR;
 my $delta = time();
  if ( $delta > $RunAt ) {
     $delta = DAY + $RunAt - ($delta % DAY);
  } else {
     $delta = $RunAt - ($delta % DAY)
  }
}

  # daemonize ... at PerlIPC
  while ( 1 ) {
     sleep RunAtTime( 4 );
     # ... your code ...
  }
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