title: Convert a string of numbers to a NSTimeInterval
body: <p>I know I must be over-complicating this because it NSTimeInterval is just a double, but I just can't seem to get this done properly since I have had very little exposure to objective c.  the scenario is as follows:</p>
  
  <p>The data im pulling into the app contains two values, startTime and endTime, which are the epoch times in milliseconds.  The variables that I want to hold these values are
   <code>NSTimeInterval *start;
      NSTimeInterval *end;</code></p>
  
  <p>I decided to store them as NSTimeIntervals but im thinking that maybe i ought to store them as doubles because theres no need for NSTimeIntervals since comparisons can just be done with a primitive.  Either way, I'd like to know what I'm missing in the following step, where I try to convert from string to NSTimeInterval:</p>
  
  <pre><code>    tempString = [truckArray objectAtIndex:2];
      tempDouble = [tempString doubleValue];
  </code></pre>
  
  <p>Now it's safely stored as a double, but I can't get the value into an NSTimeInterval.  How should this be accomplished?  Thanks</p>