In the evening hourly tours leave from the Tourist office between 7pm and 10pm.
They run on a different route to the day tours, heading out to the Casino from where there are excellent views of the the centre of Montreal at night.
The bus then returns to the city centre and does a partial loop around the old town, stopping at the Hôtel de ville where you can hop off and join a later bus.
The tour then takes a different route through the centre of modern Montreal before returning to the standard daytime route as it ascends up onto Mont-Royal for nighttime views over the city.