Best answer by woz
I think Wattbot needs another brain transplant (the first one was only partially successful).
You can switch away from your current supplier up to 49 days before the end date of your fixed term without penalty (ofgem rules), so no problem there.
Your switch into PP will usually take 17 days so if you start your switch no later than the 12th November that would be the optimum. Personally I'd allow a few days grace in case of problems as it will make little difference to be a few days early, so consider 9th-12th as your starting point.
You can't choose the day other than by timing the switch.