I'd recommend that if you need a nap midday, then nap midday.

I generally wake up around the same time in the morning, regardless of what time I went to bed. This can sometimes lead to me feeling very sleepy midday, which kills my productivity. Coffee can sometimes help, but sometimes it just makes my head even more cloudy. If I'm in a position to do so (if I'm in a location where I can lie down and I don't have a meeting soon), I generally take a short nap (~45 minutes). This brings my productivity back to normal in most cases.