When is the best time to divide?
I would divide when the flowers and leaves have died down, so in a month or two's time. Or if you prefer divide in early spring before the corms start to produce new shoots.
March usually works best in my experience
It depends where you are really. We are in the south so March would be too late for us as the roots and perhaps shoots would be up and running. The best time is when everything is dormant, when there is no snow or frost and the soil isn't swamped with water I guess.
thanks very useful info.