A couple factors worth noting, in addition to the above...
I believe that (one of) the Rick Steves travel philosophies is that Americans, in particular, have some of the shortest vacations in the developed world. We simply don't have enough time to see and do all the things we would like, and with our short vacations, on trips to Europe, it's wise to try and maximize your experiences by making good use of your time there. That usually means full days - start early, power through the day, keep moving, and by all means do enjoy the evenings, but avoid staying up too late so as to allow you to fire up early the next morning and charge out there again. It's not a debilitating, frenzied, death-march pace, but no lollygagging, not much "sleeping in." That's how his tours seem to roll and it's also how he generally suggests itineraries and activities for independent travelers in his books. I'm not much of a tour person myself, but I've come to appreciate that style of "make your days full" travel.
I'd also note that in anywhere that's become popular (and especially in places that are way too popular), the best time of the day to capture the magic free of major crowding (either with your camera or just taking in the charms) is early mornings and (to a lesser extent) early evenings. Much of Europe is at its best when 99% of the tourists are snoring away in their beds. My wife, who is a world champion sleeper who loves to get up at noon when she's not working, has finally seen the light - that is, the early morning golden light, where you can get your memorable photos without hundreds of strangers in the foreground. Last trip she didn't protest at all when I suggest setting the alarm for 4:30 AM so we could get out and spend a few golden hours taking pictures in Tallinn before the cruise ships arrived to disgorge all their passengers.
IMHO for most of us, I think the time we have to spend in Europe is the most constrained commodity we have - usually more constrained than our financial budgets. So when I'm traveling in Europe, I'm focused on being out there seeing and doing the things I came for. I get up early. I figure I can always sleep on the flight home.