If you have to ask, you aren't doing enough.
Actually if you see it as a chore,.... I dont know what to say.
Well anyways, I say whenever you feel like grabbing your bass, just have fun with it. IMO thats the best way to practice. By having fun with it, be it playing your favorite song, or just flying alover the fretboard comming up with riffs. Just keep practicing untill you dont want to. If you dont get any better or dont enjoy it, then it wasnt meant to be.
Music is entertainment! Listen to it, play it, enjoy it! Otherwise your working, and who wants to do that. Lets face it, you and I and all other musicians know that picking up the bass was our attempt at escaping from that terible reality of life called the day job. Do yourself a favor and make sure you dont make it one.
Peace
Nick