For awhile. A short while.
When I got my blue heeler, it was in the most ideal circumstance to get a puppy. I wasn't working and the entire state was under lockdown for COVID-19, so even if I wanted to, I couldn't leave him home alone. Not too long ago, life resumed and I went back to work, and our social life regained some of it's former luster. We still take him whenever we can, and make every attempt to support dog-friendly establishments when we go out. That said, we can't take him to work.
Had I known what I know now (that I'd be going to to full-time work, that heelers are insanely and inexhaustibly energetic and will literally chew the walls from boredom unless they get 4+hours of exercise every day, that eventually the world would start turning again and we'd have to leave the house...), I would be even MORE enthusiastic about my choice! Dog are great. Let me clear. ALL DOGS ARE GREAT. Dogs do not have the capacity, except through training or neglect, to be not-great. But heelers man, they are the greatest. THE GREATEST. And you're reading this. So you probably know that.
Okay, all that said: we cannot leave our heeler alone in the house for the duration of a whole work day. We do not have a farm, and he's not a working dog. His only job is to let me cuddle him, which he's very bad at, actually. I have to physically restrain him to make him cuddle me. It's not that heelers aren't affectionate, they are, on their terms - they'll lay on your feet while you pee just to keep you as close as possible, but like, zero interest in being pet or physically loved in any way. My long-winded point being, there's nothing to wear him out. He's not going to lay around and chew on a bone and nap all day and then quietly go into his crate and sleep all night. It just aint. gonna. happen.
When we need to leave the house, and the angel can't come, we do one of three things, depending on the duration of our absence:
Leave him with limited access to the house (shortest absence - 1-2 hours) We can leave our guy alone for a little while. Even better if we can get him out for a walk, first. Two hours seems to be the limit before boredom sets in, with the potential for mischief. We keep the range contained to the kitchen and hallway, with access to one toilet for refreshment. =)
Crate him (medium-length absence - 2-5 hours) I know it seems counterintuitive that he would be crated for a LONGER period of time than we would leave him out with more space, but that's because he starts chewing on non-chew-appropriate items (walls, dumbbells, etc.) after about two hours when he's either bored or irritated that he's home alone. If we need to crate him for this longer duration during the day, we make sure he gets at least a couple of hours at the dog park either before or after.
Take him to doggy day care (long absence - 5+ hours) At this point, he can't remain in the crate all day and also be expected to sleep in the crate all night. In my experience, the older they get, the less time in the crate they can tolerate without needing even more compensatory exercise.
So, yes, of course they can be left alone for reasonable amounts of time, and you may find that with time and training, your heeler can be left alone for significantly longer periods without being crated. Even if they do well alone, I encourage you to check out some well-rated doggy day cares in your area. They are great for not only tiring them out, but also for socialization with both dogs and humans. It's good to have some dog-centric relationships established in case you ever find yourself needing an emergency sitter or boarder.
Don't let a full-time job dissuade you from considering an Australian Cattle Dog as a family companion!