Trouble configuring Appointments+

Hi. I am having some trouble configuring Appointments+ to work correctly. I am configuring this for a customer (http://theonestudio.uk/book-the-studio).
This is for booking a photographic studio with two services on offer: Half Day (4hr) and Full Day (8hr) rental.
The working hours are 8am to 8pm. This should allow for 3 x 4-hour sessions and 2 x 8-hr sessions.
But this is not what I get .. What I see is slots for 8am, 12pm and 4pm whether I select a 4-hr or 8-hr session.
This is how its configured.
Time base = 240 mins
Dummy Assigned to: StudioManager
Services Configured:
-- Half Day Rental, Capacity=0, Duration=240
-- Full Day Rental, Capacity=0, Duration=480
Providers Defined - Studio Manager
-- Services for StudioManager= Half Day Rental, Full Day Rental

So essentially, there is only 1 studio, and one provider. So a user should be able to book a full day session either at 8am or 12pm. In the case of a four hour session, the user should be able to book at 8am, 12pm and 4pm. Also, combinations as available.
But this is not the case. Whether I select the Half Day or Full Day in the Services pulldown, I see availability for all three times ... for the 8 hour session! How can that be .. you should not be able to book at 8 hour session at 4pm when the studio closes at 8pm.
Over hours is set to off btw.

See the screen shots.

I am unable to get this online without this working correctly.

Thanks for any assistance in advance.

Jay