Um, I think every one of us plays that game. LOL. I'm in no position to get another dog and honestly, I don't know that I'd want 3. Especially since I live in an apartment and probably will for a long time to come. I promised myself no third dog unless 1. I own a bigger house with a yard or 2. when it's Miko's time. And since Miko's living forever, I dunno. LOL. The house w/yard is near impossible in SoCal.
However, that being said, I got Koji on a slight whim. DH and I wanted another puppy, but didn't want to find anything for a year (hmm...sounds familiar) as we just bought a condo. My breeder said she wasn't going to breed anymore and um, did we want one of her last puppies. No more breeding!!! Augh! I love her line, so um, yeah, we'll take puppy.
So, #1, don't break down and buy a puppy like I did.
As for mid-day thoughts. I would say either do as someone else stated, crate within an x-pen and pee pad, or find a good dog walker. They're out there. And I know the ones I spoke with were willing to do what I asked of them regarding "training". Heck, they even helped with training while on their walks.
I think for myself, I personally wouldn't go home unless I live down the street. When I got Koji, even 30 mins at home wasn't enough for him and me. Meaning, he either got all the time and I didn't eat lunch, or I got to eat lunch, but he didn't get enough time. I think next time, depending on the pups energy level, I may just do the crate/x-pen/pad bit. Sheltie's are smart, they will learn when to pee on a pad and when to go outside.
Just thinking out loud for my next one.....one day. But then again, if you recall, I also said I may go for show/agility prospect that didn't make it, so they're older, a bit more trained, etc.