This is a pretty good question that deserves a decent answer. I make a full time living writing, and believe me, the hardest part for me is being disciplined and making time for it.
Because I write for so many sites and my own blogs, I often have several articles that slip through the cracks or just never get published for some reason or another. For me, these are the perfect articles to turn into hubs, and since they're already drafted, it takes no time at all.
But let's assume you just do this in your spare time. I will give you two basic suggestions:
1. Just take one hour out of each day to make a hub. Even you're creating a hub from scratch, it shouldn't take you more than an hour. You can probably do two in an hour.
2. Set aside one day for hubs. If you don't want to work on hubs each day, just pick one day of the week to be the day you write hubs. Get up early in the morning and go to a coffee shop or restaurant with wifi, and spend a few solid hours writing hubs. You can probably do five or six no problem. After 4 or 5 weeks, you'll have 30 or more hubs. After a year, you'll have hundreds. Good luck!