How to remove the date information in a column, just keep time

The following will convert what you have to datetime.time() objects:

dataset['TimeStamp'] = pd.Series([val.time() for val in dataset['TimeStamp']])

Output

  TimeStamp
0  05:15:00
1  05:28:00
2  06:15:00

Since version 0.17.0 you can just do

dataset['TimeStamp'].dt.time

For versions older than 0.17.0:

You can just call apply and access the time function on the datetime object create the column initially like this without the need for post processing:

In [143]:

dataset['TimeStamp'] = pd.to_datetime(dataset['TimeStamp'],format).apply(lambda x: x.time())
dataset
Out[143]:
  TimeStamp
0  05:15:00
1  05:28:00
2  06:15:00