Assigning datetime variable to a pandas dataframe column
You've done nothing wrong.  The fact that it prints as the date without time is just a convention in Pandas for simpler output.  You can use df['Time'].dt.strftime('%F %T') if you want the column printed with the time part as well.
Storing datetimes as the Pandas type (datetime64[ns]) is better than storing them as the Python type, because it is more efficient to manipulate (e.g. to add offsets to all of them).
I have a datetime variable date_var=datetime(2020,09,11,0,0,0 ) and i am trying to populate a dataframe column for each row with this value. So i did something like df['Time']=date_var first this show 'Time' field datatype as datetime64 [ns] and not datetime and this populates Time field with value 2020-09-11 instead of 2020-09-11 00:00:00. Am i doing something incorrect ?
Thanks