My professor teaches that duration of non action should come before the verb. For instance:
On the other hand, native speakers have said both these sentences containing 已經 are correct：
Is there a difference of meaning between the last two? Or else why can 已經 render the rule my professor teaches nought? Or is the rule wrong?
EDIT: I asked the same question inside my weixin group - there sentence one was labelled 2 and vice versa! Opinions diverged greatly. Some of the longer comments are the following. Unfortunately, I don't understand them completely, because they are in Chinese:
Commentator A: 结果一样是三天无饭，但两句意思隐藏了无饭的选择关系有主动与被动，不知陆迪兄弟能否get 到.
Commentator B: 第一个含义我很饿。第二个含义我可能吃了其它食物或我还可以继续不吃饭。
EDIT 2: Two native speakers claimed that one of them emphasised time, the other not eating. But they disagree as to which is which.