I'm using Buiodda's craft's sheep shearing (which I believe comes from Rain's Clothing v3), and one part of the recipe is
{[NEARBY_TILE:ground]} 'During midsummer'
This sort of works in that most of the year shearing is not permitted. However, the timing seems to be wrong, as I failed to shear my sheep last year because the recipe claimed the time was wrong, despite UrW showing the time as being midsummer. I was late in shearing due to being caught up in other tasks (as well as not trying before UrW claimed it was midsummer), so I probably tried it after the midsummer point. This year I tried to make sure not to make the same mistake, so I've tried shearing way too early, and managed to shear the sheep at day 1, 9 weeks before the midsummer point. It thus seems the timing actually results in summer before midsummer (but it didn't work a few days earlier, so the cutoff may well be 9 weeks).
A question then is whether it's a deficiency of the mod script or if the mod indication is off, i.e. a bug in UrW's mod support?
I'll try shearing after the midsummer point to find the approximate cutoff time at that side, but it will be some time before I get there.