The tour is a hop on hop off bus tour - so you can either stay on for the whole round trip or get off at places of interest (see other journal entries).
There is an English speaking guide and recorded English narration on all the popular sights.
The only downside is the fact that the schedule is a bit hit and miss - all they'll tell you is that buses are meant to arrive every 25 mins - sometimes they arrive sooner, sometimes later (depending on traffic jams etc) - so you can't do this tour if you're on a tight schedule.
You have to purchase hop on/off tickets from your hotel before boarding - if you're just staying on the bus for the 2hr 30 min circuit you can buy tickets on the bus.
It starts at around 8.30 until 11.00pm