I guarantee that doing a 6 am and 10 am (or 11 am) training cycle each day, provided you had the time to do it, is a very effective training strategy. The first workout opens up your capillaries and raises your core temperature so that the second workout is very good quality with VERY LITTLE perceived stress.
Additionally, the 3-4 hours time between the two workouts allows you to hydrate and put some carbs in your body. To do this right, as soon as you finish the first run you must hydrate and consume your breakfast. You can't wait around. Ideally you need about 3 hours between the end of your food consumption and your next run, in my opinion. OF course, you would want to NOT over-eat!