def invalid_timestamps(invalidation_stamps, invalidate_cut) :
    
    """
    Helper function for invalid_timebins
    
    Return a dataframe with the timestamps, for which all timebins in between have to be invalidated
    """
    
    invalidation_stamps['timediff'] = invalidation_stamps['timestamp'].diff().fillna(0).astype(int)
    
    return invalidation_stamps[invalidation_stamps['timediff'] > invalidate_cut]