Bionic if you can give them some form of shelter they will probably dry off enough for you to spray them but keep them in after spraying so it dosent get washed off. Short, sheared fleece drys quickly. Also, if they have been sheared they should be at a much lower risk of flystrike though head flys might be bothering them.
I find my lambs are susceptible to strike despite spraying but my sheared ewes dont seem to be bothered although I do spray them. If their bottoms are clean and the weather is keeping the flies at bay then I'm sure that waiting until the sheep dry will still be in good time.