If you plan things out right, it's easy to make an animated film even if you have a full time job or other such bad habits that otherwise monopolize and occupy your free time. Work nights are perfect for doing these small interstitial shots that have minimal action involved in them. Lip syncing is the most work involved, and if you plan things out well enough (and don't fall into a beer induced stupor too early in the evening), you can crank out 10 to 12 seconds in a single 4 hour evening.
Keep in mind, 4 seconds per day average is the rate to keep up. That's what I've found over the years of doing the Rocketmen vs Robots series, and Archon Defender. So on my days off I work on modeling new sets or characters as the shots come up, or animating the shots that have 20 people getting blown up with explosions everywhere and 30 different particle effects to tweak, and 80 layers in After Effects to deal with.
Days like this are easy: 2 layers, 4 second shot, 2 seconds of lip sync. No big deal... time for a beer ;D