I have road riding out my door, but I sympathize with you when I'm feeling like riding on dirt. The closest decent trail to my house is about 8 miles away, however it is conveniently on my way to work. When I want to MTB, I take my bike and riding gear with me to work, change at work at the end of the day and then hit up the trail on the way home. When I lack time I do speedwork to get a good workout. I don't know if that helps you any. I know what it's like to be time crunched. I'm trying to fit riding while restoring a large 250 year old farmhouse and studying for a professional licensure exam. I never have much free time, but on the other hand, I'm never bored