Pretty much the same (not that productive any time anymore, sigh).
I do best in the morning, but can usually survive until about 4 PM when my back says "no more".
Mornings, and I am fine till 6P.M. or so then I am done.
It used to be around 4:00 p.m. After I retired 23 years ago I slowly became a morning person so now it's first thing in the morning (sometimes before sunrise).
Mornings! By mid afternoon my IQ has dropped 35 points.
Mornings, I start fizzling out around two in the afternoon.