Here is the way I would do it:

{
   local $ENV{TZ} = 'EST';
   print scalar localtime(), "\n";
}
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This is UNIX specific and you might replace EST with Canada/Eastern or some other name so EST or EDT will be used as required.
Another approach that is more portable, but only works it both timezones use the same meathod for day light savings is

print scalar localtime(time - 4 * 60 * 60), "\n";
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