Simple JavaScript I just can't get to work

Question

Hi guys I'm new here and to JavaScript really but I have had a go at trying this and it simply wont work for me. Basically I am creating a time-card for my work and because most people dont use military time the total calculations for each day have to take this into account. So I tried to make a script that would +12 if the total number of hours was less than 0; however it doesn't seem to work and still shows the negative number even though I have scripted it not too. I have attached the script bellow and if anyone could assist me it would be greatly appreciated.
// Start Time
var v1 = getField("Text1").value;
// Finish Time
var v2 = getField("Text2").value;
// Lunch
var v3 = getField("Text3").value;
// Total Hours
event.value = v2 - v1 - v3;
if(parseInt(event.value < 0 )) event.value = (parseInt(event.value) + 12).toString();
many thanks

Answer 1

Are the start and end time values being treated as numbers or strings by JavaScript?
What is the formatting of the field?
// Start Time
var v1 = getField("Text1").value;
// Finish Time
var v2 = getField("Text2").value;
// Lunch
var v3 = getField("Text3").value;
// Total Hours
event.value = v2 - v1 - v3;
if(parseInt(event.value < 0 )) event.value = (parseInt(event.value) + 12).toString();
console.show();
console.clear();
console.println("v1: " + v1);
console.println("type of v1: " + typeof v1);
console.println("v2: " + v2);
console.println("type of v2: " + typeof v2);
console.println("v3: " + v3);
console.println("type of v3: " + typeof v3);
Using civilian 24 hour time format for the fields, I get the following result:
v1: 9:00
type of v1: string
v2: 17:00
type of v2: string
v3: 0:30
type of v3: string
The calculation results in a NaN value.