'Given a start and end session label, returns the distance between
them.  For example, for three consecutive sessions Mon., Tues., and
Wed, `session_distance(Mon, Wed)` would return 2.
Parameters
start_session_label: pd.Timestamp
The label of the start session.
end_session_label: pd.Timestamp
The label of the ending session.
Returns
int
The distance between the two sessions.'

def session_distance(self, start_session_label, end_session_label):

    start_idx = self.all_sessions.searchsorted(self.minute_to_session_label(start_session_label))
    end_idx = self.all_sessions.searchsorted(self.minute_to_session_label(end_session_label))
    return abs((end_idx - start_idx))
