Container-grown azaleas can be planted any time of year, provided they are watered properly....the exceptions would be frozen ground, or ground to wet to dig without ruining the soil structure (my own winter).

The shallow rooted plants are going to dry out fast in summer heat and will need careful attention to watering along with a mulch of the root zone to cool roots and conserve moisture.

Of course you could always take advantage of the sale, bring them home and put them in afternoon shade (watching the containers closely for adequate moisture), and plant them when the temperatures cool a little in a few weeks.