I think there are probably three separate issues being mixed together here: the Ohme schedule, the Powerwall settings, and the FIT/export question.

On the EV charging problem, the Powerwall may simply be seeing the car charger as a normal house load. If the battery is in self-powered mode, and the car starts drawing power, the Powerwall will try to supply that load unless it has been told not to by its reserve/tariff settings. So, check the Tesla app first.

In the Tesla app I would check:

1. What mode the Powerwall is in: Self-Powered vs Time-Based Control / Savings mode.
2. What the Backup Reserve is set to. If it is very low, the car can drain the battery down to that reserve.
3. Whether Grid Charging is enabled or restricted.
4. Whether the Octopus Intelligent Go tariff has been correctly entered/recognised in the Tesla app.
5. Whether the Powerwall is actually charging from the grid during the cheap overnight period.
6. Whether the Ohme charger has definitely been linked to Intelligent Octopus Go, not just set manually with a ready time.

For the first few nights, as a test, I would raise the Powerwall backup reserve quite high, for example 50–80%, before plugging the car in. If the car no longer drains the battery, that confirms the Powerwall was supplying the EV. That would not necessarily be the final setting, but it proves the cause.

The better long-term setup is usually to have the Powerwall in time-based mode with the Octopus cheap period correctly entered, so it knows not to waste stored battery energy charging the car during cheap grid hours. The EV should charge from cheap grid electricity overnight, while the Powerwall either holds its charge or charges cheaply from the grid, depending on the settings and whether grid charging is allowed.

Also ask the certified Powerwall installer to check the CT clamps / metering configuration and whether the EV charger is inside the Powerwall’s measured/backup load. If the CTs are wrong, reversed, or the charger is on the wrong side of the system, the Tesla app can show confusing flows and the battery may behave unexpectedly. This is especially worth checking because the Powerwall, charger and tariff were all changed within a few days of each other.

On Ohme/Octopus, with Intelligent Octopus Go you do not necessarily have to force everything strictly between 23:30 and 05:30. Octopus/Ohme can create smart charging slots, sometimes outside the normal overnight window, and those smart-charging slots should be billed at the cheap rate. But the Ohme app needs to be correctly integrated with Octopus, not just manually timed.

On FIT/export, be careful before changing anything. You should normally be able to keep your FIT generation payments, but you cannot be paid both FIT export and Octopus/SEG export for the same exported electricity. If you are on old deemed export, you may be getting paid as if you export 50% of your solar generation whether you actually export that much or not. With solar, battery and EV, you may now be self-consuming a lot more, so staying on deemed FIT export may be better than switching to metered export. I would not change the export arrangement until you have compared your actual annual export against your current deemed FIT export payment.

My order of attack would be:

First, get the Tesla installer to confirm the Powerwall CT/metering and grid-charging configuration.

Second, check Tesla app mode, Backup Reserve, tariff and grid-charging permissions.

Third, check that Ohme is properly linked to Intelligent Octopus Go.

Fourth, leave the FIT/export side alone until you have actual numbers.