title: How to subtract 2 times with moment.js, then subtract some minutes
body: <p>I need to subtract 2 times with moment.js (get the difference), and then with that result, subtract some additional minutes (simple int). It's for calculating timesheets. A few examples:</p>
  
  <pre><code>Example #1:
  Start time: 10:00 AM (represented in js as "10:00")
  End time: 2:00 PM (represented in js as "14:00")
  Lunch: 30 minutes ("30")
  Expected result: "3:30" (10am - 2pm is 4 hours, minus 30 minutes for lunch = 3hrs 30 mins -- and I need it output as "3:30")
  
  Example #2:
  Start time: 6:15 AM (represented in js as "6:15")
  End time: 4:45 PM (represented in js as "16:45")
  Lunch: 0 minutes ("0")
  Expected result: "10:30"
  </code></pre>
  
  <p>I know moment.js can do this but I'm struggling to get expected results. I've been trying this:</p>
  
  <pre><code>function getTimeInterval(startTime, endTime){
          return moment(moment(startTime,"hh:mm").diff(moment(endTime,"hh:mm"))).format("hh:mm"); 
  }
  </code></pre>
  
  <p>The formatting seems right, but I'm getting incorrect values. For example, the result returned for my example #2 is "6:30" instead of "10:30" <strong>And then how do I subtract off int minutes for lunch?</strong></p>
  
  <p>Any help is much appreciated.</p>