I think for myself, the key is knowing that the guy who biked across India wasn't writing a novel. Or at least, he wasn't biking across India, writing a novel, and maintaining a 40+ hour job and raising a family.
I'm a husband, father of two kids, am involved in my church, and own a house with a yard. So, "contributing to open source" and "writing every day" or "learning a new skill" is #5 on my list. Probably further down the list if I think about it.
That said, I think it is possible to do _one_ of those things well on a regular basis. Right now I'm learning a new programming language. Before that I was reading a number of books.
Bottom line: it starts with knowing your own personal bandwidth limits, and knowing your prioritizes. Then backfill with the rest.