You didn't mention what you were a half pound short of, but I assume you have a 3 pound bag of DME and needed 3.5 pounds. DME is 1.046 gravity for a pound per gallon and honey is around 1.042. Two cups of honey weighs 1.5 pounds, so adding .013 or so to a 5 gallon batch compared to the .005 that you lost from the missing .5 pounds of DME. Looks like a little boost, but no big deal.
I have used honey before and did not notice a longer fermentation, but I used only half your amount.
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