68F is fine.
How about something like this:
64% cold water
0.04% ADY or 0.03%IDY (given the small quantity, I would dissolve either is a bit of tepid water - taken from the formula water and warmed to around 100F)
Mix until generally smooth and homogenous - 3 or 4 minutes in a mixer is probably plenty. It wonít get completely smooth and silky yet. It will still have a bit of a rough look when you stop the mixer. Itís going to feel somewhat tacky and rather soft. Dump it onto a counter, give it 15 or so kneads until it is fairly stiff, cover with plastic or a bowl, and let it rest for 7-10 minutes. It will have relaxed noticeably. Stretch and fold it 4 or 5 times. Watch this video if you donít know what I mean by stretch and fold: http://www.gourmet.com/magazine/video/2008/03/bertinet_sweetdough.
It will get stiff again and get some tears on the surface. Cover and let it rest again for another 7-10 minutes. Remember to try to capture air in the dough as you do your stretch and folds. Give it a few more stretch and folds. If it is now silky smooth, youíre done. If not, give it one more rest and a few more stretch-and-folds, and you should be good to go.
Bulk ferment for 2 hours then divide and form into balls. Let rise for 22 hours or so. Keep an eye on it for the last 8 hours or so. You can speed things up by putting them into a warm (115F-120F or so) oven or slow things down by putting them into the fridge for 20-30 minutes.