If you keep them consistantly watered they should survive but may look really crappy, they are quite hardy. I know that plants bought now and planted can grow quite a bit if well taken care of, so you should be able to get some decent growth during the summer if you trim off the old growth. If you planted them in organic amended soil and watered every couple of days it would help

Careful with mulch. You could rot them. Pine boughs are the mulch of choice around iris. Allows the air to circulate. Few people mulch iris at all ever. If they do it's very light or they pull it away from the plant itself. Iris really don't like constant moisture. Anything that is going to hold real moisture is likely to cause a problem. Further east you go the more of a problem. Personally I'd put a dark rock on the them to hold heat and prevent heaving. Mulching would be the kiss of death here. Experiment a little you might figure out what works in your area. If you already have some that weren't disturbed much you have a failsafe. I've tried cold frames, foundation plantings, rocks, mulch. Potting them in a cold room works best this late. Others worked Ok. Potting worked better. New England is also very wet compared to WI. All my iris except for a few extremely tough oldies are in raised beds or have drainage trenches dug around them. It's going to rain here now any time from Now until snow and then most of April and May. I will be redirecting water and snow run off until the end of June. Last snow usually disappears here around May 1st. Temps aren't usually a problem once established. Moisture in late fall and spring is. Best mulch is good snow early on before the frost goes too deep. I hate snow but find myself praying for it from the end of October on. Got rain?

It depends on the plant :-) I've divided some in the middle of winter (eg: hostas, daylilies, Siberian iris) with no ill-effect. OTOH, both agastache and penstemons tend to prefer really good drainage and sometimes have issues with our winter weather. Agastache in particular I would tend to leave be until spring and drier conditions. FWIW, the rule of thumb in the timing of dividing perennials is to divide early blooming perennials in fall and later season perennials in spring. But that's pretty general and there are always exceptions.

I never have had a problem with dividing or moving irises at any time... That's been our experience. Only found four ways to kill them: 1. replanting in a low/damp spot where they rot, 2. not moving them soon enough after falling into year-round total shade from surrounding growth, 3. not watering enough after transplanting during late summer drought, and 4. forgetting to replant/give away divided rhizomes..... hate finding those forgotten boxes or pots. Assumed question was about the rhizome types, but same for Dutch bulbs. Just harder to locate them for dividing once foliage dies back in the late spring . American Iris Society mentions getting them moved a month+ before the first hard freeze, so may be different with the harder freezing further north.