Student or Learner
"This procedure(in medical term) can only be done once every one year or six months".
Would it be correct to say every "Procedure can be done once 300 days or one year"?
Using 'only' means you have to choose one time period or the other. 300 days is neither six months nor a year.
But how to use it with days? Like 300 days.
It can be done only once every 300 days.
Which of course averages out to approximately only once every ten months.