Getting a date-time field and returning just the time in a different format

Getting a date-time field and returning just the time in a different format

I'm currently trying to write a script where it grabs a date-time field, reads only the time, and changes the time to a new time from a time field. So far this is what I have: 
  1.  eventTime = rec.Start.getTime();
  2. eventTime = eventTime.toString("yyy-MM-dd","HH:mm:ss");
  3. info eventTime;
  4. newHour = input.New_Time.getHour();
  5. newMinutes = input.New_Time.getMinutes();
  6. newSeconds = input.New_Time.getSeconds();
  7. newTime = newHour + ": " + newMinutes + ":" + newSeconds;
  8. newTime = newTime.toString();
  9. info newTime;
It's currently returning the time  but I'm trying to figure out how to change the time. I first tried the toTime() and toString(), but it's not changing the format of it.
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