title: Offset epoch date by timezone and hour:minute
body: <p>My user picks a date, which I store in epoch seconds (or milliseconds if necessary).</p>
  
  <p>Separately my user picks a time of day and a timezone.</p>
  
  <p>How do I adjust my epoch time with this new information. I feel like I should be able to add X milliseconds based on the hour/minute and then subtract based on the UTC offset of the timezone, but maybe there is a method that does this for me already</p>