Got my five green leaves a few weeks ago, but did not choose my reward (50 SCs) until yesterday as my membership year expires 30 April and I preferred to have the status credits count towards this membership year.
The status credits came through almost immediately, and on the website I now have 5 grey leaves which suggests these have "reset". (On the Qantas app on the other hand it still shows 5 green leaves and the option to choose my reward, which I already did yesterday, so the Green Tier details on the app and the website have obviously not yet synced.)
The "Green Tier achieved" message bar states that my benefits are accessible until 30 April 2023.
I have just gone used the Rewards Store to buy a $25/3200 QFF point charity redemption and a 130 QFF point "make a (climate) positive contribution" item. Will update this thread if and when two of my grey leaves turn green as a result, which should confirm that it is possible to get 2 x 50 SCs for achieving Green Tier in a single membership year. (Though in my case it will also require the quiz to come back as I don't intend to buy wine or stay at an eco lodge.)
edit: Just noticed that my post is essentially a long-winded repeat of ChrisMars' post immediately above. *sigh*