I have Octopus Agile which charges my car overnight between 1230am and 04.30am! for 5p per kw/h for other times its 13.4p
Ian are you sure you are Octopus Agile and not on Octopus GO, the Agile tariff has the night off peak rate, then a variable tariff, but has a premium rat 16.00 -19.00 which attracts a 35 pence kWh tariff.
I am on the Octopus Go tariff like you 5p kWh off peak, 13.72kWh day unit rate, 25p day rate
Unfortunately I have suffered a brain injury and occasionally I get confused and often say the wrong thing.