Ok, my fingers are cold so I'll type to try and warm them up.
Question: When is the best time of day to exercise?

Noon(ish)-
The sun is out (usually), the temperatures are warmer, and your muscles, as fueled by breakfast (you did eat one, didn't you?), are finally warmed up and ready. So what's stopping you from doing your exercise routine during your lunch break? The most obvious is the "sweat factor" especially when your workplace has no shower facilities. Well, I wouldn't recommend doing a strenuous workout if you are meeting with high-level clients at 1 or something, but it definitely is possible to workout during lunch and still look presentable afterwards, sans shower. A towel is a big help. The other key are baby wipes/wet wipes. Now, they do tend to smell like powder or flowers so I'm not sure what if that's exactly right for you manly men. But in a pinch, a towel and some water works just fine.

The biggest problem I've encountered with running during lunch is the time restraint. I feel like taking the entire hour is sort of pushing it, since it tends to be workworkwork at my office most of the time. Coworkers have expressed much surprise upon seeing me in running clothes (or "jog togs" as my supervisor calls it) and asked me (a bit peevishly), "You actually have time for that?" I normally like to go running for 6-10 miles at a stretch, but with the 1 hr time limit I have to be sure to fit in time for a stretch and cleanup, which means (for me) less of a workout. Another problem, of course, are the unexpected meetings, emergencies, and other work-related business that pop up last minute. So, while your energy levels are at a maximum and the weather is at its' prime, the mid-day timing may not work for everybody.

Afterwork/night-
This has never worked well for me, though there are benefits. If you like having a workout buddy, nighttime tends tobe the best time to meet up. It also seems easier for most people to swing by the gym at this time. Since the gyms are packed, this could be good motivation as well.

Scientifically, your body has been working all day and burning/processing all your food intake into energy. So you have lots of fuel to keep you going. Also, your body is more efficient at converting metabolites into energy, so you're less likely to feel tired.

However, there's just something about it being the end of the day that, well, tires my mind out. I don't know about you, but after work, just want to go home, cook, eat and sleep. But again, other people may seem the afterwork workout to be a great way to burn off the daily stress and to relax.

That's my spiel for now. As many of you have pointed out, exercise at ANY time of day is beneficial, so why not get started now? Have a great workout and have fun!