DataFrame where Date is datetime:
Column | Date
:-----------|----------------------:
A | 2018-08-05 17:06:01
A | 2018-08-05 17:06:02
A | 2018-08-05 17:06:03
B | 2018-08-05 17:06:07
B | 2018-08-05 17:06:09
B | 2018-08-05 17:06:11
Return Table is;
Column | Date
:-----------|----------------------:
A | 2018-08-05 17:06:02
B | 2018-08-05 17:06:09