pd_date=pd.read_csv("path/file.csv",index_col="created_at")

user_screen_name
created_at
2019-02-22 03:27:07      ...
2019-02-21 23:10:38      ...
2019-02-21 19:09:57      ...
2019-02-21 17:17:45      ...

2019-02-22 03:27:07           year-month-day hours:minutes:seconds

user_screen_name
created_at
2019-02-22       ...
2019-02-21       ...
2019-02-21       ...
2019-02-21       ...

str(pd.to_datetime('now').date())

'2019-02-22'