Signs I'm about to ovulate are my body temperature (I also get these with af too) and I also get an achy back and seriously bloated stomach. For me OV is much worse than AF, so much so I actually can't wait to get back on the pill. Luckily it's all for a good cause. Literally before I OV, my stomach is so bloated and painful (bottom of belly) and it just feels like a dull ache, sometimes it can hurt to walk. I can tell as soon as OV has finished as it all just disappears. Weird sensation. Everyone is completely different though. It may just be minor things you could begin to notice like body temperature, or it could just slip by without you knowing. I've read so many things about it and it just boils down to everybody being different.
I think early evening would work too, I think the only reason they say not first thing is because it's diluted over night with what you have held in.
Here's hoping you get results soon xx