i am not pure domaining, if i have 8hours to work online, i'll use to watch auction, buy and sell my domain portofolio, also after that i try to build a blog for long term monetization (i am not domainer, just like domain)
If lets say I would agree to this proposition of working 6 to 8 hours on domaining then the major part of it would spend on structuring marketing campaigns.
Just domaining? I'd probably do some shopping (forums, drops, auctions..etc), send out some end user emails (and hopefully be replying to lots of others), list and/or manage auctions that I might be holding on different sites..
The hardest part is sitting on a big domain, literally sitting down waiting for an offer or a bid. If I dedicated that much time to domaining daily, I'd probably spend the majority of the day reaching out to potential end buyers.