When do I know my pup is ok to be left in a room alone uncrated?

All my dogs where at least a year or older before I trusted them to be out of the crate alone. Although it depends on the dog. If I were you though I would just keep him safe inside the crate for awhile longer, especially because at 6 months his bladder is still not totally developed.
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He might get into a chewing phase too, which is something to consider. Sometimes pups get bored and tear stuff apart when put in a room alone.
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My dog is just over a year now and we still have to crate her. It is not because of using the floor as a toilet, but she chews up tons of stuff. You should definitely take that into consideration and if you want to try leaving him/her alone, you should put him/her in a barren room with nothing valuable in it and alot of chew toys. (no rugs either- hard to clean)
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When everything is OK at weekend, when you can watch him, it should be OK in other days too.
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Could be up to 18 months before you can leave them out all day. If yours is still having occasional accidents, then he is still to young to be left out.

What you need to do is test him on weekends when you don't work. Leave him out while you go for a short walk. Next time, go for about a hour. Slowly work the time up that you are gone. That way you know how long you can trust him.
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He is still quite young but could learn to hold his bladder with more training and time. Do a trial run and leave him in his room for a day and see what happens. You could also leave him in the room for a few hours at a time then go back home during lunch or a break to let him out. My dog wasn't trust worthy until he was older, about a year old for 8 hours at home.
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Oh you have a dog that isn't reliably house broke as yet..not a good sign for allowing it the freedom while you're gone. I don't even think about allowing a dog freedom when they are under a year..too much puppy in them still. I actually decide when the might be allowed freedom by the individual, and I go in small doses, short periods of time and small areas, gradually increasing time and area until I know without a doubt they have the training down reliably. I consider all training, not just using the house as a bathroom, and I wouldn't even consider a dog who is still having accidents.

In all fairness, at 6 months of age I'd take a step back and try to examine what I could do to get the dog reliable in house breaking. At this point I'd consult with a trainer as a one on one basis. The worst mistake people make in training IMO is 'rushing' it. GL
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I have a very well behaved 17 month old Bichonpoo. Like your dog she has the occasional accident. She was 9 months old before I left her out of the pen at night and only in the last week do I leave her out of the pen when I am not home. The reason wasn't that I didn't trust her or that I was afraid she would have an accident the reason was that as well behaved as she is the reality is she is still a puppy. Puppies have a natural curiosity about things like light cords, furniture, pillows etc. My dog has NEVER chewed anything that she wasn't supposed to but what if she and choked when I wasn't home? Once she proved to me that she could sleep for 8 hours or so outside the crate and not let curiosity get the better of her I knew she was ready to do it when I wasn't home.
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