We run the tup near to and in sight and smell of the ewes for three weeks, then put him in for 3 weeks.
Last year was the first time we had any empties (two gimmers; all 3 experienced ewes took and held), and then we realised we hadn't done the "proximity teasing" last year.
Seasonality / when the ewes will cycle is affected by genetics, geography, climate, weather, previous lambings if any, as well as pheromones. I have noticed many times that a given ewe will often lamb on the same day year after year, and her daughters often fall into the same pattern. But if you put a maiden adult ewe with a tup, she'll cycle and lamb unseasonally, and ditto if a ewe has had a year off (for whatever reason).
I prefer to put the tup out late November so they lamb mid-April onwards. We've pretty much always got some good grass and decent(ish) weather by then, any earlier and we're often short of grass and/or lambing into sleet, hail etc. We're only producing for ourselves and mostly give all lambs two summers, plus later borns often catch up earlier ones anyway, as their mums were in better shape and had more milk from the get-go, and the earlier little ones spent the first week or two coping with the cold and not really growing.