So, today I decided to experiment and give it a try. My schedule and the weather actually worked to allow me to get two runs in. Here's how it went:
Before work: 3 miles in 27:15
After work: exact same 3 miles in 26:29
So I beat my morning time by exactly 46 seconds. (Maybe I should start running in the evenings.)
6 miles total, and although my legs felt slightly heavier in the evening run, my body was much looser and I felt faster. For the morning run it took my the entire first mile to wake up and feel loose. I don't know what time of day is the best to run or train, and frankly I don't think it makes a great deal of difference (although I do think there is some wisdom in doing your training runs around the same time that your actual race will occur, usually mornings). I don't plan to regularly do 2-a-days (mostly because of scheduling), but I kind of liked having a time to try to beat from earlier in the day, and I would like to do this type of running at least once a month.
It's great now that the weather is getting warmer, I'm seeing a lot more people outside now, even other runners sometimes. Where were they all winter??