Twitch.tv/ReseroNetwork
It's their latest video. unfortunately I don't remember exactly what time they recruited him, but once they do they keep him in the party. It's also after he recruits Sera. I think about midway? Hopefully that helps.
And yeah, he headed to Orlais and then back tracked to the hinterlands where he recruited Blackwall. I don't think it's that far in the game.. he was like the 2nd character recruited, behind Sera.
It doesn't look that far if you forward the story, but I pretty much wanted to halt the story and recruit him before doing anything. Now here is a very important question that I need answered after watching some of that stream (haven't gotten to the blackwall recruitment part yet) and other gameplay vids.
It appears Iron Bull has two ways of getting recruited or at least for the player to know about him. One is to go straight to the map he's in and stumble upon him, OR apparently if you don't do that, one of his mercenaries lets you know he exists (happens when Leliana tells you about Blackwall). So, with that in mind, is this also possible for Blackwall? Will we be able to recruit him early if we stumble on his recruitment spot on the Hinterlands map?