There are many iris, with different requirements for the seed - so a rough answer to your question would be 30-365 days to germinate. I find many will germinate at a higher rate if give a warm moist period preceding a moist chill, then brought back to slightly warmer (55ish) for germination. At the very least, most will germinate better with at least the moist chill, minimum 8 weeks. Then there are the exceptions, I sowed iris chrysographes a couple of years ago and had the pots at room temp for a warm moist period, planning to put them outside (January) for the chill in my mild Z8. They germinated within a couple of weeks in my office and I was then committed to caring for them under lights until Spring.