A. As long as your vine is growing vigorously you can continue to prune through the summer. You want to make sure the berries are shaded by the leaves to prevent sunburn.
We trim the vines back several times during the growing season. Usually table grapes are more vigorous than wine grapes. When the vine is shading itself or out of control it needs some pruning or thinning of its growth.
This is something new grape growers to the desert discover too late. They think you can grow grapes with trellis systems from more mild climates. Wrong, wrong, wrong. This is a very harsh climate and the sun can be very damaging. Grape bunches must be protected from intense direct sunlight.
Use grape training systems that provide crop cover as they are maturing.