Right now the ones responsible for peer reviewing have been Crossbones+ members but Drew moves them from Draft to Under Review. Moderators also have the ability since they too are vetted. However, there is nothing that designates a reviewer as "expert" so for us peer reviewed refers to the fact that the article probably isn't total bullshit. Of course, the community at large tends to smack down the articles that do tend to be very flawed.. it does provide some visible feedback for reviewers as well.
There is no timeframe for being under review. Drew and I spoke about whether or not there should be some sort of "meh.. it's probably okay" state an article is in but staying in the "under review" state tends to be that.
Also it is possible that for recent articles that they have been approved and are "Under Review" but have a publish date set to sometime in the future. This is just to spread out the information flow and make sure that your article gets some frontpage time for people to comment on it and review it.