Oooh, I see you've charted info for the whole month, although only just started temping! That's a little more useful in predicting when you O'd

It seems perhaps you would have O
'd on the second of your two possible dates as your CM wasn't really indicative of O around the 31st.
My gut would say you're about 9 dpo but of course without the temps it's difficult to know for sure...
Either way, to answer your question, the small drop today wouldn't really be enough to indicate af was on her way... but then some women don't experience the drop until af is already here so it's one of those 'it's different for us all' things - frustrating, I know!