title: Time-barred list in redis
body: <p>It's easy to do a list in redis with a fixed size, by performing <code>ltrim</code> at the required size. However, how can one maintain a list that contains data that is time-barred, not size-barred. </p>
  
  <p>E.g. how would I maintain a list of all <code>user_ids</code> that logged into my website in the last 10 mins? Please provide an illustrative example of the most efficient way to accomplish this. Maybe I'm approaching this with the wrong data-type?</p>