Make it a DatetimeIndex first:
pd.DatetimeIndex(montdist['date']) + pd.DateOffset(1)
Note: I think there is a feature request that this could work with date columns…
In action:
In [11]: df = pd.DataFrame([[1, 2], [3, 4]], columns=['A', 'B'])
In [12]: df['date'] = pd.to_datetime(['21-11-2013', '22-11-2013'])
In [13]: pd.DatetimeIndex(df.date) + pd.DateOffset(1)
Out[13]:
<class 'pandas.tseries.index.DatetimeIndex'>
[2013-11-22 00:00:00, 2013-11-23 00:00:00]
Length: 2, Freq: None, Timezone: None
In [14]: pd.DatetimeIndex(df.date) + pd.offsets.Hour(1)
Out[14]:
<class 'pandas.tseries.index.DatetimeIndex'>
[2013-11-21 01:00:00, 2013-11-22 01:00:00]
Length: 2, Freq: None, Timezone: Non