Great news - have checked the app, and if you go to 'book lido swims' (NOT 'book family swim' or 'book lido lane swimming' ) you can now book a two hour session (starting 9.30am, 12.30pm or 2.30pm). 200 spaces available per session.
Whole pool open, no lanes during the daytime... but if you want to swim in lanes, there are still loads of 1-hour sessions morning and evening. Lido opens 6am at the moment so it's all lanes for 3 hours until 9am each morning (last bookable slot is 8am). And similar from 5pm weekday evenings.
It's a shame that (as far as I know) you still have to book via the app, and I'm not sure if you have to book children separately (looks like under-7s included in the adult ticket), but in terms of maximising the numbers of people able to visit, I think they've done the best they could at the moment.