I do quite a bit of local shearing. Most people do their shearing in the spring. That is books and old farmers recommendation.
Time of shearing is actually more of a personal choice. I have long wool sheep so am continously shearing at home, but for those who have to hire a shearer, picking a time that works for you and your shearer is imperative.
While spring shearing has many benefits and is preferred, I want to point out some advantages to getting on the fall shearing schedule.
#1 The shearer is not as rushed. This makes it easier for you to get a day and time that works for you and the shearer. Not to mention they will have a bit more time to go over flock health with you and just general life happenings.
#2 More room in the barn. In the Northeast, most shepherds house their sheep solely in the barn over the winter. Having the fleeces off the sheep creates more room in the pens and at the feeders.
#3 Easy of lambing. While spring is generally the time small flocks lamb, a lot of commercial flocks try to have a fall lamb crop as well. Fall shearing makes lambing easier in the late fall and early winter.
#4 Less moisture in the barn. Let's be honest wooly sheep create a humid environment. Taking away the bulk of the wool reduces the humidity. This lessens the chances for upper respiratory problems and other health issues in the barn.
#5 Checking overall flock condition. We pasture our sheep over the summer. As we bring them in like most shepherds, we like to check over body condition on our ewes. Having them shorn makes this easier. Even if you do not summer pasture, fall is still a good time to check body condition before going into the winter months.
These are only some bullet points on fall shearing. I still recommend talking with your local shearer on their recommendations. Some have a fairly busy fall schedule or only travel in the spring.