title: float values to time that includes nulls
body: <p>I have columns with time as float values. the columns also have null values that I want to keep since by removing them deletes other dimensions I am interested  in in my table. because of the null values i am not able to transform the the values into strings before converting to timestamps.</p>
  <p>I am using this code</p>
  <pre class="lang-py prettyprint-override"><code>def Format_Hourmin(hours):
          if hours == 2400:
              hours = 0
          else:
              hours = &quot;{0:04d}&quot;.format(int(hours))
              Hourmin = datetime.time(int(hours[0:2]), int(hours[2:4]))
              return Hourmin
  </code></pre>
  <p>Is it another one that uses floats?</p>