Having Googled the original poem, there's really only one place you could split it into two stanzas, which coincides with repetition of phrases from the first stanza - the only repetition in the poem - and which is where the poem switches from thinking about Monday to it being Sunday at midnight. I don't think the author put the pause there purely to save her breath...
(you can read the original poem - typeset without the stanzas - and the original questionable high school questions here http://www.jiskha.com/display.cgi?id=1394137792)
It's also worth noting that even if the assumed authorial intent is completely wrong (like many other theories of authorial intent attributed to authors who usually aren't around to question it), it's a far more reasonable interpretation than the other multiple choice answers. Though this doesn't really apply to some of the other examples
This is the crux of the matter. James Joyce (just to pick someone whose work is heavily discussed) may have made a reference to a common Catholic belief and not realized it because he was embedded in Irish Catholicism. It could have made some metaphor stronger or weaker. When you discuss the metaphor you may be discussing the author's unwitting intent. Thus the author themselves might not be the proper authority (except for their own overt motivations).
Literature isn't special in this regard -- after all we go to psychiatrists & therapists to help us learn about our own actions that we don't understand.