I don't think that Tempus needs to have put kryptonite in the other dimension with Kara. He's not there to make sure it hurts her or Clark, after all. All he needs to do is destroy Herb's beacon so they can't return.
Given that Herb was expecting Lois and Clark to return only a half an hour later, why on earth did he feel the need to answer the door? He doesn't need a back story or excuse for why he's at their house. He just needs to stay in the secret closet until they return.
I'm not sure how good a shot Herb is, but I suspect that he wouldn't be that accurate. His position is really compromised by Tempus's belief that he won't actually shoot him. Maybe he could shoot Tempus in the leg or something non-vital. I guess that could still kill him by bleeding out, though.
I suppose that could be true but he did say that the celebration was due to the deaths of Superman, Lois, and Utopia and that it had already happened or would shortly.
I still suspect that Herb can take his pompous behind out, I mean if Bernie can in Nan's Home Series (Home: Circle of Fate) then Herb should not have too much trouble handling him. He just needs to find a lamp to hit him over the head with...
I actually expect a lot of twists and turns as Debbie is only just under 1/3 of the way through this story.
Mike