Just called Octopus to see if I could switch over to their Go Faster tariff (4 hours a night of cheap electricity). Bit annoying that you need to go onto the fully variable first (68p/kwh and 25p standing charge) - for up to 16 days! Can see this becoming a headache...
Won't take them long if you have the SMET2 meter, Go is 4 hours @7.5p time 00.30-4.30AM, Go Faster is 5 hours @ 8.25p can start from 9.30pm.
You chose your 5-hour time to start Go faster, any time from 9.30 to just after midnight.