title: Time manipulation in ruby
body: <p>I want to create a DateTime instance that lies 20 minutes and 10 seconds in the future.
  I tried around with Time and DateTime in irb, but can't seem to figure out a way that really makes sense. I can only add days to DateTime objects and only add seconds to the Time objects.</p>
  
  <p>Isn't there a better way than to always convert the time I want to add into seconds?</p>