How to remove the date part and still keep the data type as datetime64[ns]

Question

Can someone please guide how can I remove the date using pandas and keep the datatype as datetime64[ns]:

0    2023-01-02 11:00:00
1    2023-01-02 16:00:00
2    2023-01-02 14:00:00
5                    NaT
6    2023-01-02 12:00:00
7                    NaT
8                    NaT
9    2023-01-02 13:30:00
10                   NaT
18   2023-01-02 09:00:00

TIME OBSERVED        datetime64[ns]

I tried to find something on Youtube but havent found anything very specific.