Hi I have very exciting news. TL;DR: I was able to reverse engineer the protocol and put everything into a Homeassistant App/Integration 
I posted more infos here: Diivoo / Tuya / Smart Home Hose Water Valve - #11 by Stefan_G
Hi Stefan, this was awesome information! Whilst I don’t have any RF version of this water timer, I have the older bluetooth (BLE) version (Haozee branded). Turns out I was able to reuse the DP instructions, and remove the cloud dependent wifi-ble gateway, in favour of an extremely simple esp32-c3 based gateway (just a simple esp32-c3 supermini is all you need!). Because it’s a different use case, I’ve created a new repo that caters for the BLE wifi gateway instead, and credited you for the original reverse engineering.
Here’s the repo: GitHub - tsjoa/esp32-c3-BLE-gateway: an esp32-c3 based bluetooth low energy gateway that can control a water timer, like the diivoo... · GitHub
Hope it helps somebody down the line, and get rid of the tuya dependency of their water timer (and maybe some other wg02 dependent smart devices).
Thanks again, Stefan!