In math terms, when you do a division problem, dividing gives you the quotient and taking the modulo gives you the remainder. Here, dividing a number of seconds by 3600 and dropping the decimal gives you the hours. Taking the modulo gives you the remainder of seconds:

my $s = 7209; # 2 hours and 9 seconds
my $hours = int $s/3600;
my $seconds = $s % 3600;
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