It depends largely on your reason for cutting back. The hardest cut back done on azaleas is usually the complete removal of all branches to generate new ones once the trunk has been developed. If you want to cut back that hard, then I would wait until the tree is growing vigorously again after its repotting. In real time I suppose that would be no sooner than the year after you repotted it.
leaves are the food factories so: No leaves = no root growth. Conversely, roots supply the raw materials to build and maintain leaves, so: No roots = no leaf growth. You need to find a balance between the two extremes. If you have taken a lot of root out with the repotting, then the tree will need energy to grow more root and I would not take too much of the top out. If it was only a root 'trim', then you could afford to take more out, but again, only after the tree has shown signs of good recovery.
The above applies within the normal bounds of repotting/root pruning. Things change at the far extremes. If you have taken too much root out, then there won't be enough to support the top and you'd need to cut back quite hard just to keep the tree alive.
A short version would be: If you want to prune the tree hard, then wait until it is vigorous (however long that takes). That way you know it will have the energy to back bud well. If it has been repotted into a good mix (or well sifted kanuma), the nature of azalea roots means it will be some time before you will need to repot again, so you have time to play with.