Leave in ground two weeks. Should see lots of eyes if you dig then. Washing them off helps to see the eyes. Steve in Baltimore County.

We've had several frosts and I've cut down masses of dahlias.. I don't know that I'd wait two weeks (it won't hurt) but you shouldn't need to wait that long. I've cut one day and dug the next and had no problem seeing eyes. Just think and look for 'pimples' on the collar area surrounding the stem. They tend to be light yellow/white or sometimes pinkish, raised swellings on the collar.

The biggest mistake people make is chopping off the tubers at the neck. You really need to stab into the hard collar area to get some tissue behind the eyed-up area.
Eyes marked in blue. Green part is the main stalk of the plant around which the collar with eyes forms.
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I want to get it done so will do it this weekend. If I can't see eyes I will just store them whole.