They can be divided in the spring. I often start mine in early April, and at that point after a few days laid out in a growing medium, the eyes become VERY apparent. Either fall or spring dividing works, although I personally believe that the fall is the best time to divide, but the spring is often easier.

Store whole clumps and look for eyes in Spring as Jroot says or, just go ahead and guess at division now. If you think there might be an eye on a decent tuber, save it. I mark those "?Eye?" If it turns out to be a dud in warmer weather, not much was lost but a bit of time cutting it. You also don't waste much time waiting for a dud to sprout (as I do every Spring.)

I did something I hope will work. Like you I have been waiting for the usual frost that hasn't happened. I took all my tubers up last weekend and cut the stalks down to about6" long, bundled them up with like types together in paper bags and bound them. Then I hung them stalk side down - or upside down to cure. We are finally supposed to get some colder weather this week. I read the dahlia society pages and all their recommendations but I know I'm having 15 people for THanksgiving dinner and I have a lot to get done before and it sure looks like if I followed the Society's directions I'd be out there with the turkey digging tubers. I read on the P. Allen Smith website he recommended taking the tubers up and hanging them upside down for 4-5 weeks to cure. So I thought I'd try it. I don't know if I'll let it go 4-5 weeks because then I'll be running into Christmas and I just know me - I won't get it done and it will bug me. Hope this works!