Down to 60 or even 50 depending on wind, I just wear shorts and a long sleeve top. Below 55 to 50; I wear a neoprene ear band, light-midweight running pants (tapered pants, not tights), mesh underwear, silkweight thermal base top, midweight half-zip top, then an outer layer per weather conditions- wind/water resistant if needed. Once it's in the high 30's I add smartwool liner gloves, and a full lightweight beanie. That's my setup down to about 20 degrees; below 20 I add a balaclava. Below 15 I add silkweight leggings under my pants, heavier crew length socks, and warmer underwear. Below 10 I stop running because my feet start getting too cold (never happens in Baltimore). No magic time in the morning- cars are going to hit you in the middle of the day too- be defensive. I usually run at night, but sometimes early AM (6AM)