title: Pandas DataFrame: Convert Integer time hh:mm
body: <p>My DataFrame which contains </p>
  
  <pre><code> dep_time   sched_dep_time
  0   517.0   515
  1   533.0   529
  2   0.0     0.0
  3   544.0   545
  4   1.0     101
  </code></pre>
  
  <p>I want it to be in 5:17 , 5:15 as departure and scheduled departure times, NaN are filled with 0's also 1.0 indicates departure at 1:00 
  Tried following </p>
  
  <pre><code>flight_data['dep_time']=flight_data['dep_time'].astype(str).apply(lambda x: 
                          pd.to_timedelta(x[:-2] + x[-2:]+':00'))
  </code></pre>
  
  <p>Value Error :expecting hh:mm:ss format, received: 21 days 13:00:00.000000000:00
  I am even not sure of how dep_time like 0,1,2.. should be converted. Thank you and appreciate your help  </p>