print(dt.index)
# = DatetimeIndex(['2018-01-01 20:00:00', ..., '2018-01-03 04:00:00'],
#                 dtype='datetime64[ns]',
#                 name=u'DateTime',
#                 length=385,
#                 freq=None)

my_axis.plot(df)
print(my_axis.get_xlim())  # = (736695.72708333354, 736697.14791666681)

# vs

df.plot(ax=my_axis)
print(my_axis.get_xlim())  # = (25247280.0, 25249200.0)