Any time in September or October, as long as the ground hasn't frozen. Some people say earlier is better in our climate so the bulbs can develop some roots before winter sets in. I usually aim for Thanksgiving roughly.

Irises you want to do right now (gives them time to establish roots before freeze up). With Asiatic lilies I've planted them right up to Halloween.

Wow I totally didn't read that, sorry! Fall bulbs are actually tulips, hyacinths, daffodils etc. that have to be planted in the fall. That's what I was referring to.

I have always planted lilies in spring but if Sharon says it's okay then plant them in the fall. Irises should be planted now, for sure.

You can plant lilies in the spring too, I do prefer to plant the Orientals/ OA's/ OT's/ L.O. Hybrids in the Spring, gives them a whole season to set good roots to make the winter. If you are planting these hybrids in the fall, make sure you put a good layer of straw mulch down for their first winter. But with your regular hardy Asiatics, they can be planted spring or fall here in the far north.