Here's a bit of video included in «The Cove» that illustrates the level of mental acuity of dolphins: (dotearth.blogs.nytimes.com)
That you have increased mental acuity for about half an hour to two hours after... or almost immediately sorry immediately to about two hours after consuming it after which you have a big slump. (blog.bulletproof.com)
Probably 16 to 24 hours into it and so you can definitely have an increase in mental acuity in a buzz from fasting for about 16 to 24 hours into it. (blog.bulletproof.com)