One way to do this would be to adjust $thistime appropriately.

sub time { # ** conflicts with builtin 'time'! Yow!
  my $thistime = shift;
  $thistime -= 3 * 3600; # - three hours, since GMT+3 is that much ear
+lier.
  my @a = gmtime($thistime);
  ...
}
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You should probably look at the strftime function offered by the POSIX module, it may make stringifing the date and changing it's format in the future simplier.