Of course, they're expecting an emphatic "NO, disturbing the plant will shock it".
At Wildwood, we transplant all year round. Moving a plant from a container to the ground often does the plant a favor. The ground is cooler than a container, the drainage is better, and it can be done with very little disturbance to the roots.
In this Sonoma garden, a combination of shade umbrellas and shade cloth will provide relief from the 100 degree temperatures. The plants have their root zone bubblers for [extra] water and should pass through summer with flying colors!