For what it's worth, I just got my first bill from Octopus and it's 100% accurate.
I kept track of all my charging slots and the bill has charged the cheap rate for each half hour slot where any amount of charging occurred. This is for all household use.
Interestingly, the Ohme picks slots in 15 minute increments so I've had many instances where the Ohme picks say, 10.00 to 10.15 and then 10.30 to 11.00, Octopus charges the cheap rate for 10.00 to 11.00.
Octopus give you an average cost per unit of electricity which for me was 12.2p.
Overall I'm very happy.