Back the the Linkshell Ether was running, a person called Avien Talasi made themselves a reference picture for the elements.

This is it:
http://i.imgur.com/8VawE.png

Basically it shows the elemental day and the conquests (Astral) and the submissions (Umbral). If memory serves, and my memory could be wrong, a conquest would cause itself to be more powerful during the astral periods and a submission would cause what it affected to be weaker during an umbral period, with both of these effects being reversed in some manner or other during their out-of-polarity periods.

This was mostly taken with respect to crafting and a recepie's elemental harnessing, but now I'm wondering if their could be a time-of-day affect on these spells as well.