Yes, but it was three days later than "at the latest". So I immediately jumped through Octopus's hoops to apply for the tariff. At the end of it all I got a message saying this normally takes about 14 days. So big sigh, and knowing my luck they probably mean 14 working days.
Then while I was away for a week's holiday I noticed something odd in the app, which looked as if I'd been charged over £2 for electricity on a day when the house was empty and there should have been minimal usage. Oh well they'll sort it out, I thought. Then two days later I realised that was actually an export payment to me. It had kicked in only four days after my application.
It's so nice to look at all that export and smile, rather than fuming that I'm not getting paid. And of course I'm having to reverse all my routines, to charge the car and the battery at off-peak rates so that I export as much as possible.