One thing that I learned from Marathon training is that running is on my schedule. That means that weather it's before work or after 3 meetings -if it's a day to run then I have to run.
And I discovered on those 6 O'Clock runs after a 10 hour day-they are often the best and I always feel better after than I did before.
So no matter how tired you are-make an appt. somewhere in your day with yourself and work it out!