From my observation, the most you normaly get on clear black ice in very cold conditions is about 1.25" ice formed per day. In some cases if it has been windy and very cold the water can be super cooled but not yet frozen, and when the wind drops it snaps in very quickly and uniformly and grows very fast the first night. On great pond in Belgrade ME one year it was open water and windy friday at dusk, The wind died around dusk, Several of us walked the lake the next morning~ 12 hours after it froze. and sailed it 36hours after it froze. That was a one time in 10 years thing. Generaly my rule of thumb is you can walk it gingerly 36 hours after it skims if it is black and hard. I take an ax and won't explore the ice unless it is 1.5" thick. I will set up my boat when the average ice thickness is 3" and the thinnist spots I find are 2.5".
I use Bob Dill as my goto guy for ice questions.
http://lakeice.squarespace.com/ is a great read about ice, ice safety, etc.
