It's OK to buy potted blueberry plants in the summer, but it might not be such a good idea to plant them now. You could keep them watered, and sheltered from the most intense sunlight between 10 am and 4 pm. Morning sun and late afternoon sun is good. Just focus on keeping the shrubs alive and healthy, and transplant around September 15 to October 15. At that time, the days are shorter, the shrub is beginning to go dormant, and it will not become stressed by the transplant procedure.

Hmm.
If you're having issues with the plants drying out or baking in those pots, I'd sure expect that those issues will be abated, significantly, by getting them in the ground, mulching well, and watering as needed.
In the pots, daily watering may not even be sufficient, depending upon the medium they're growing in - if it's mostly peat, it may dry out pretty rapidly - and be difficult to get fully re-wetted.

Potted plants out in full summer sun should have their pots shielded from the sun to keep them cool, especially if they are black nursery pots. I have wooden frames that set pots in. It blocks the sun and allows air flow around pots. At a minimum I would wrap the pot in something that doesn't conduct heat well (insulator). If you simple put them in the shade they might not get enough sun.

Even with the pots shaded it will be difficult to keep them hydrated. You want some kind of water reservoir, such as tray on the bottom. Nursery pots don't have this. Even then you might have to watery twice a day, especially in August. Constantly watering with tap can also be problem for some. The tap water I have is alkaline, and the plants don't like too much of it. I try to water with rain water when I can.