alt Hacker NewsHave you seen the schematics for these boards? They are exceptionally simple. Many devkits are much more complicated.
I have actually done embedded engineering in the past and I was being generous with "a day." Skimming a datasheet is a skill and it certainly will not take a day to get the information you need off of it.
If you mean the HW alone... Still over a day. If you mean the software to go along it, a couple orders of magnitude more.
Even the simplest peripherals can bite back if you are not careful and you don't test the edge cases. AVR's are indeed quite simple, but if you try to build stuff other people will use, things need to be polished.
I actually do embedded engineering. I'm doing it right now! More on the SW side than the PCB design side, and, again, this is quite an exaggeration from your side, saying you could do it in a day.