Sounds like you have a date, such as "2006-08-03" and need to convert it to something that ensures that "2006-07-31" is 4 times the distance away that "2006-08-02" is. Assuming "day" as the unit, then it would be exactly four away. Sounds like what you want is:

  my $epoch_day = int($datetime_obj->epoch / 24 / 60 / 60);
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Perhaps I'm missing something, though ;-)