I often post on Facebook my success -- or more often my lack thereof -- in getting up in the morning to go for a run before work. In all fairness, it's harder than you think, especially when you are training for a marathon. For the record, I'm not the only runner who faces this challenge. Many of my running friends have to walk the line between sacrificing sleep and getting in their required run.
To figure out if it's even worth putting on your running clothes, you have to work backwards. Let's say you start work at 9am and your average door-to-door commute is one hour. Let's say you also take 30 minutes to shower, dress and otherwise get ready for work.
If you run a 9MM (Minute Mile) and want to get in a 5 mile run before work, you have to be up and out the door, hopefully in your running clothes by 6:45am. As an 8MM, I can sleep about 5 minutes longer. I also can get ready for work in less than 20 minutes providing it isn't a Shave Day. On the other hand, I tend to hit the snooze a few times so that quickly negates any extra time.
Keep in mind that you probably should factor in some cushion time into your pre-work run. You cannot assume you'll finish your 5 mile run at whatever pace you normally run. It might even take you longer to shower and get ready since you're a little tired from running 5 miles. And woe is the day when all of this plus issues with your commute make you extra late for work.
Trying to sneak a run in during lunch is even tougher because while you may not have to worry about the travel time, you probably cannot fudge much beyond the 1 hour lunch and you definitely should shower. So somehow you have to change clothes (twice), run and shower all in an hour. Not realistic unless you can run really, fast or have a flexible boss/work environment.
It works the same in the evening. You leave work as early as possible but you cannot control how long it takes to get home. You donn your running clothes before you talk yourself out of it and head out. Let's assume leaving work at 5, get home at 6 and have your act together enough to get back out the door by 6:15pm. You finish your run by 7 and then a quick shower gets you ready for whatever is left of your evening by 7:30 ish.
Which brings up the next point. This is based on a relatively fast runner. If your running pace isn't what might be considered Speedy Gonzalez territory, then you either have to get up earlier or run fewer miles. Most avid runners agree that it isn't worth the effort of donning running clothes to run anything short of 3 miles and if you are training for a marathon, your daily mileage shoots past that fairly soon.
So if you are lucky enough to have a flexible work schedule, take advantage of it and run when you can. Otherwise, make the effort to get up in the morning and catch up on sleep by going to bed earlier, so deal with the fact that your evening is gonna be shorter than you'd like because you are making up mileage.