Hi Alessandro,
Excel usually wraps hours > 24 into the next day.
You would be better off calculating this as a number as an Excel date number as follows:
my $date = ( $hours * 3600 + $minutes * 60 + $seconds ) / ( 24 * 60 * 60 );
Then write it using write_number() with a suitable format.
That will handle the wraparound automatically.
John