Well, it turned out OK after all (I think).
I was mixing batches of about 2 cu.ft. at a time in my small mixer. I didn't use any slump tester, just eyeballed it. The first couple batches were probably stiffer than normal and the last few probably a little looser than they needed to be. In any case, it's been almost a week now and I'll probably wait the full 28 days before taking my temporary supports out and putting weight on it.
Nealtw, I think I'm safe with that 45 deg stress cone. There is 14 inches between the column and the edge of the footing. Including the 3.5" curb on top, I have 15.5" of concrete depth.
Now, just 4 more to go.
Thanks for all the input.