You could use a module that supports fractional time.

use Date::Tie;
tie my %d, 'Date::Tie';
print " $d{hour}:$d{minute}:$d{second} \n";
$d{frac_hour} += 1.1;
print " $d{hour}:$d{minute}:$d{second} \n";

  02:22:04 
  03:28:04
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