Why morning versus evening rides? There is so much less traffic at 5AM than at 8 or 9PM. I have been out to Concord by 6AM and fewer than 15 cars passed me in the 12 or so miles on my route. And those drivers are much less likely to have an after-work-drink in them. And it fits my schedule. I have been doing early morning runs and rides for years and my body seems to have no trouble getting out that early for exercise.
It is a fairly odd experience riding in the dark. On dark roads your vision is restricted to the illuminated oval from your light. You can look up at the moon in the sky but if you do you might miss the bump in the road, or an animal that is crossing your path, or veer off the road and any of those would mean trouble. It still is a fun and interesting experience although riding fast is really not all that possible, except on well lit streets. I did ride over into Lexington for a 15 miler that I did at 17mph, which might not seem fast during the day but it does seem fast at night. I also did an early morning ride on the bike path in a light rain at 12mph and that seemed fast enough for me. So you do get a workout but not like you might on a morning in early July. And on longer rides you experience sunrise and that is never a bad thing.
Might animals cross your path? It happened this morning, for the first time. I have seen a million rabbits, some raccoon, and other smaller creatures, including domestic cats. They were very aware of me and stayed out of my way and I gave them room. But today my top tube was hit by something that I saw cross the path from my right in Bedford. I felt it hit the bike but it did seem to have any heft to it. It seemed like a shadow, it was so small and was not directly lit by my front light, but I am guessing it was a bird. I stopped to look for it but saw nothing so I am assuming that it survived.
Besides the light, or lack thereof, there is also the issue with temperature in the early morning. As the season gets on, morning rides might mean temperatures in the mid 40s, which is close to my limit for a lengthy ride. I have done rides this fall that I really need a shower after but not because I had been sweating but because I am chilled and need a very hot shower to warm up. It is getting late in my cycling season and while there might be a large number of good cycling days left, I might be working or otherwise busy and miss most of theme. I have plans for at least one ride in Western Massachusetts late this month but that is highly weather dependent: rain cancels and temps below 40 degrees (in the hills) cancels. So I will continue to try to get out early as long as I can manage it and try to be ready for those one or two long rides that I have time for.
My bike in Bedford. I had my light on my helmet today, which is on my rear rack with the light still on. You can also see the red glow from my flashing rear red light, and reflective sidewalls on my Panaracer tires. I was also wearing a reflector vest and have reflective material on my cycling shows. I think I am well lit: