title says it all, help?

He's in his tent opposite Lasota.
https://youtu.be/P43Um72HYSM?t=260

I don't see him there, does that mean I've waited too long to do the quest?

What your journal says? It might be too late if you progress too far in the main storyline.

The journal seems to think I've finished it in that the son died and the father told me even though he was unhappy with me.

But the quest isn't marked finished and when I choose it the quest text on the screen tells me I still need to challenge latande.

Is it because I went forward with the conspiracy quest perhaps?

That's probably it, it looks like you're not alone in this: http://steamcommunity.com/app/20920/discussions/0/540735426468693277/
I guess the quest is unfinishable right now.