Now I have finally been moved onto the Octopus Go tariff, I can confirm that the charger does NOT solely charge within the cheap tariff times.
In addition, despite the faqs saying it uses the battery capacity and current charge level to determine the best period to charge within, this is inaccurate.
What I have found is that if you set a ready time for 07:00am, with a multi-tariff configuration set to 00:30-04:30 and 04:30-00:30 the charger will start at 00:30 but carry on charging right up to 07:00. This is despite the fact you might not want to charge right up to the cars set limit (ie 80%). There is no technology in place for the charger to know the current level, it simply carries on charging until the car tells it to stop.
The only way to guarantee you remain within the cheap tariff is to set the ready time for 04:30.
Perhaps I misunderstood originally what was going on, but the wording on the site could be written much better.