Octopussy also do a 5-hr 'Go', at a slightly higher (currently (sorry) 8.25p/kWh vs 7.5 p/kWh for 4 hours); with 'Go' you choose your timeslot; Gofaster (5 hrs) allows a slot from 01:30 to 06:30, enabling you to battery pre-heat and ac precondition in the last hour at the 8.25p rate. Maybe worth the +0.75p/kWh increase if you're commuting/early starting a lot?
The battery-pack is a sizeable mass, and once heated, although obviously losing temperature at a rate dependant on oat and wind speed,, will likely retain maybe +10 deg C an hour after heating. I've noticed that the app won't switch on battery heating if it's been run 90 mins before (might be just a comms bug, but has been consistent); an obd data readout would confirm all this - probably someone on the forum has real data (?)
atb