Translation:We swim for half an hour every day.
So I and ended up finding this in another thread on duolingo. (sorry for the guy I quote, I forgot your name, please forgive me)
the explanation is here : https://www.digmandarin.com/chinese-separable-words.html
see section (3) of "The common usages of separable words"
I hope this helps, It did for me
That’s the model solution as far as I can see. (Or maybe the solution was changed in the meantime?)
I put "every day we spend half an hour swimming" to reflect how often Duo Lingo marks me incorrect for not saying "spend" whenever recounting how long an activity took (and I was still marked incorrect). A consistency check would be recommended.
"We swim for half of an hour every day" is actually better English grammar, but it said I was wrong.