Thanks for quick around ankur, Please find the below client script and script include

we are using the fields strt_date/en _date using "glide_date_time" type and duration field type is "glide_duration"

client script:

var strt = g_form.getValue('strt_date');

var end = g_form.getValue('en_date');

if(strt != ' ' &&end !=' ' && newValue != ' '){

var ajDur = new GlideAjax('scriptinclude');

ajDur.addParam('sysparm_name', 'cal');

ajDur.addParam('sysparm_start', strt');

ajDur.addParam('sysparm_end', end);

ajDur.getXMLAnswer(function(answer)){

g_form.setValue('duration', answer);

});

}else {

g_form.setValue('duration', ' ');

}

}

Script include:

cal : function(){

var startDate = GlideDateTime(this.getParameter('sysparm_start'));

var endDate = GlideDateTime(this.getParameter('sysparm_end'));

var dur = GlideDateTime.subtract(startDate, endDate);

return(dur);

},