Calculating between two times to get total hours

I did a lot of research and almost have the below working.  There are 3 issues

1. When I do a half hr it calculates as a whole number, i.e I have 1:00 - 2:30 shows 1.30 rather than 1.5

2. When there is no data it shows 24 hrs.  I want it blank

3. When I put in 0:00 - 0:00 it shows 0 hrs.  I want it to show 24 hrs. 

I appreciate your help.

if ((this.getField("End").value.length == 0) || (this.getField("Start").value.length == 0)) {
event.value = " 24.0";
}
else{

// get the values of the fields
var sStart = this.getField ("Start").value;
var sEnd = this.getField("End").value;
var sDate = "1-Jan-1970 ";

// compute only if we have values
if(sStart != "" && sEnd != "");

// add a formatted date value to the time field values
if (sStart > sEnd) {sDate = "2-Jan-1970 "}
sStart = "1-Jan-1970 " + sStart;
sEnd = sDate + sEnd;

// convert the date time strings to date object
var oStart = util.scand("d-mmm-yyyy h:MM tt", sStart);
var oEnd = util.scand("d-mmm-yyyy h:MM tt", sEnd);

// convert date object to milliseconds since 1-Jan-1970
var nStart = oStart.getTime();
var nEnd = oEnd.getTime();

// compute the difference in milliseconds
var nDiff = nEnd - nStart;

// convert to seconds
var nSeconds = Math.floor(nDiff / 1000);

// compute the whole hours from the minutes
var nHrs = Math.floor(nSeconds / (60 * 60));

// compute the remaining minutes
var nMins = (nSeconds / 60) % 60;

// set field value to the difference
event.value = nHrs + "." + nMins;
}