We start shearing in late May if any have a rise, and continue into June until they are all done. OH hand shears and it is much easier to do once there is a rise, and produces a better quality fleece for craft workers.
We don't shear our lambs/hoggs until they are over a year old as they live out, but sometimes if they are to be housed over the winter it can help to reduce pneumonia etc for them to be shorn in the autumn.
We apply Crovect to the hoggs starting in May, but we simply watch the adults very carefully for signs of fly interest, and crutch if necessary, but don't apply the Crovect until after shearing - as they are hand shorn it can go on directly after shearing, whereas when sheep have been machine clipped it is better to wait to apply the anti-fly-strike product until there is some fleece regrowth for it to stick to.