title: Getting the time interval
body: <p>I have two timestamp input one is the current time and another one is future</p>
  
  <p>i.e.</p>
  
  <p>Future time:  2010-8-17 23:00
  Present time: 2010-8-15 11:00</p>
  
  <p>I want to setup notification system which will display the time intervals between the above dates. i.e.</p>
  
  <p>15 minutes before
  30 minutes before
  1 hour before
  2 hour before
  3 hour before
  ....
  ....
  ....
  1 day before</p>
  
  <p>I am not sure how to achieve this task in php, wondering if any one here can suggest me how to achieve this task</p>