I agree with the "anti-hardcore" approach of keeping the time commitment and mental energy commitment manageable. You can do it more than five five-minute periods per week, though, with the following techniques:

• Leave the banjo out of its case and easily accessible at all times, reducing the activation cost of playing it. You can just walk by and, on a whim, pick it up and play it for half a minute. (This may not be practical if you live with a toddler or if your living space is extremely small.)
• If you don't already have one, get a strap, so you can play while you stand or walk.
• If you watch TV or do other stuff that doesn't occupy your hands, noodle around on the banjo at the same time.

How much you can do these depends on your husband's tolerance for noise, but it may help to play quietly, or mute the strings with the side of your hand, or play only with your fretting hand.

Bonus tips:

• Chords are the thing you're most interested in now, but don't be afraid to mix it up with single-note stuff.
• Play along with things, be they random bits of music you hear on the TV, radio, or internet, or your favorite recordings. This is hard at first but gets easier the more you do it. Don't worry too much at first about playing exactly the same thing you're listening to; just try to approximate it or, failing that, find something that sounds good with whatever you're listening to.
• Noodle. Play random stuff. If you find something that you like the sound of, play it over and over, and come up with variations.

What style of banjo do you play? My brother Mason plays clawhammer on a five-string open-back banjo. On most of his YouTube stuff he's playing guitar or viol, but he plays banjo in this video of "Rove Riley Rove" (which also includes yours truly [mandolin], and our sister Katari [voice] & my friend Curt [guitar]).