If you can keep up with watering them for the first year, whenever you have a shovel in your hand and the ground is workable, then you can move the perennials. The problem in the summer and during the first winter is lack of adequate watering. The disturbed root systems can't take up enough in dry soil conditions to support the top growth and if you cut the top back too much the plant can't produce enough food to regrow the damaged roots.

Aha! I gardener that works on my time-table! We farm, too. :) I always seem to be planting and moving stuff later in the spring than is really best. Here's what I do. The day before the move, I water deeply and let the plants get a really good drink. Then, spray with wilt-pruf, let it dry, transplant and water in well. Most things hardly miss a beat this way. I'm doing some moving and dividing now.