title: Adding seconds to timestamp in a defined interval in R
body: <p>I've a dataset with ID and timestamp.</p>
  
  <p>Each ID mostly has 12 observations of time stamp for each minute.
  I 'm having a hard time adding 5 seconds interval to each timestamp for each minute. </p>
  
  <pre><code>Actual Data                     Desired Format
  
      ID       Time           ID        Time     
      4466    12/1/14 19:56   4466    12/1/14 19:56:00
      4466    12/1/14 19:56   4466    12/1/14 19:56:05
      4466    12/1/14 19:56   4466    12/1/14 19:56:10
      4466    12/1/14 19:56   4466    12/1/14 19:56:15
      4466    12/1/14 19:56   4466    12/1/14 19:56:20
      4466    12/1/14 19:56   4466    12/1/14 19:56:25
      4466    12/1/14 19:56   4466    12/1/14 19:56:30
      4466    12/1/14 19:56   4466    12/1/14 19:56:35
      4466    12/1/14 19:56   4466    12/1/14 19:56:40
      4466    12/1/14 19:56   4466    12/1/14 19:56:45
      4466    12/1/14 19:56   4466    12/1/14 19:56:50
      4466    12/1/14 19:56   4466    12/1/14 19:56:55
      1136    3/23/15 23:00   1136    3/23/15 23:00:00
      1136    3/23/15 23:00   1136    3/23/15 23:00:05
      1136    3/23/15 23:00   1136    3/23/15 23:00:10
      1136    3/23/15 23:01   1136    3/23/15 23:01:00
      1136    3/23/15 23:01   1136    3/23/15 23:01:05
      1136    3/23/15 23:01   1136    3/23/15 23:01:10
      1136    3/23/15 23:01   1136    3/23/15 23:01:15
      1136    3/23/15 23:01   1136    3/23/15 23:01:20
      1136    3/23/15 23:01   1136    3/23/15 23:01:25
      1136    3/23/15 23:01   1136    3/23/15 23:01:30
      1136    3/23/15 23:01   1136    3/23/15 23:01:35
      1136    3/23/15 23:01   1136    3/23/15 23:01:40
      1136    3/23/15 23:01   1136    3/23/15 23:01:45
      1136    3/23/15 23:01   1136    3/23/15 23:01:50
      1136    3/23/15 23:01   1136    3/23/15 23:01:55
  </code></pre>