df = df.sort_values(by='DateTime1',ascending=True)
>>> df.sort_values(by='Date') # This now sorts in date order
Date Symbol
0 2015-02-20 A
2 2015-08-21 A
1 2016-01-15 A
# Descending Date Values (Highest to lowest)
df = df.sort_values(by='Date',ascending=False)