I have been leading this kind of lifestyle for quite some time. I work very long hours, so my sleeping hours at night is actually quite short. But I made up for it my taking penguin naps during working hours.
My current job do not require me to work long hours. I almost always can leave by 7pm. But I am still used to my penguin lifestyle.
Productivity today is quite bad. There's a few times when I feel sleepy and can't think properly. Normally, I would nap for 5 minutes and wake up fresh and able to continue work at a much faster speed. But no, I can't nap now. My manager doesn’t like it. So I have to struggle to keep awake and have my groggy mind try to do the stuff at 1/10 the speed. Grr.
I know, I can solve all these problems by sleeping early at night so that I won't be sleepy in the day. But I've being a penguin for so long. It takes time to adjust back. And before I do, I can solve the sleepiness problem in 5 minutes but I can't use that method, so I use the rest of the day method. Grr.