title: How to split pandas record with one large timedelta into multiple records with smaller ones?
body: <p>I have a dataframe with 3 columns: timedeltas (duration) of time slot, datetime of slot start and datetime informing when record was created. Timedeltas are all multipliers of 15 minutes:</p>
  
  <pre><code>Index    duration    slot_start         creation_time
  
  1.       15 minutes  some datetime 1    some datetime 3
  2.       45 minutes  some datetime 2    some datetime 4
  </code></pre>
  
  <p>What I want to achieve is:</p>
  
  <pre><code>Index    duration    slot_start                      creation_time
  
  1.       15 minutes  some datetime 1                 some datetime 3
  2.       15 minutes  some datetime 2                 some datetime 4
  3.       15 minutes  some datetime 2 + 15 minutes    some datetime 4
  4.       15 minutes  some datetime 2 + 30 minutes    some datetime 4
  </code></pre>
  
  <p>Is there any tool for such operation? How to achieve it easily and time efficiently on very large dataframes?</p>