title: Sidekiq perform_at specified datetime
body: <p>I'm using the SideKiq Ruby gem and I want to use </p>
  
  <p><code>perform_at</code></p>
  
  <p>From the wiki I read that I can use </p>
  
  <p><code>perform_at(3.hours.from_now, 'mike', 1)</code></p>
  
  <p>...Is there a way to use </p>
  
  <p><code>perform at</code> </p>
  
  <p>on a specific datetime? For example, if I save a variable </p>
  
  <p><code>datetime = 2014/Apr/16 22:30</code></p>
  
  <p>could I just write something like </p>
  
  <p><code>perform_at(datetime, do_something)</code> </p>