import numpy as np
import pandas as pd
from datetime import datetime
dates = [datetime(2011, 1, 2), datetime(2011, 1, 5), datetime(2011, 1, 7),
    datetime(2011, 1, 8), datetime(2011, 1, 10), datetime(2011, 1, 12)]
ts = pd.Series(np.random.randn(6), index=dates)
ts
Selecting the first index after a certain timestamp with a pandas TimeSeries