Calculate Time difference between two times

function convertToMinutes(time)
{
var parts = time.split(":");
var hours = parseInt(parts[0], 10);

var minutes = parseInt(parts[1], 10);

var totalMinutes = hours * 60 + minutes;

return totalMinutes;
}

var heure1 = this.getField("date3").value;
var heure2 = this.getField("date4").value;

var cminutes1 = convertToMinutes(heure1 );

var cminutes2 = convertToMinutes(heure2 );

if(heure1 != "" && heure2 != "")
{

// Calculer la différence en millisecondes
var difference = cminutes2 - cminutes1 ;

// Convertir la différence en heures et minutes
var dheures = Math.floor(difference / 60);

var dminutes = Math.floor(difference % 60);

// Afficher la différence
console.println("Différence : " + dheures + " heures et " + dminutes + " minutes");

event.value =dheures + "h:" + dminutes + " mm";

}
else {
event.value = "";
}

Please post the code for the "parseTime" function. 

Are there any error messages posted in the JavaScript Console window. 

In fact, this code is exactly the type of thing that you should be testing and debugging in the console first, before using it in a form field.

You'll find a video tutorial here on using the Console Window:

https://www.pdfscripting.com/public/Free_Videos.cfm#JSIntro

Might be helpful if you let us know in what way it's not working, exactly...