Via <diveduration> the duration of the dive is given in seconds as a real number. If the profile data are given inside <samples> it isn't necessary to indicate <diveduration>, too. If the profile data are unknown, it is a good idea to set the <diveduration> (if known).
<dive>
<dive>
see also <dive>
<!-- duration of dive 1 h 13 min --> <diveduration>4380.0</diveduration>