For those in which piano is a second instrument, how long is your practice time?

I'm planning to spend 20 minutes a day. I hope that will be enough for me to be able to comp at jam sessions or big band rehearsals as a back-up, and use a MIDI keyboard to enter music into a music notation program.

Since I'm already a musician and have used piano as a tool, I'm thinking this may be enough. Any thoughts?

I took a couple of years worth of piano lessons many years ago, in order to gain what I called "functional piano skills" (for arranging and composing). I found a great teacher who was willing to head down any jazz theory path I wanted. It was great fun, and very useful for me.

At this point, though, I could probably work up fairly simple pieces, but my kids (ages 9 and 11) play better than I do. They just don't have the many years of musical experience that I have.

As far as practice time goes, I don't have a recommendation. Or at least a tangible one. I'd recommend that you figure out what kinds of skills you need to work on (for example, basic comping) and then practice accordingly.

I'm spending more time on the piano initially while I still have the time before I get fully back to formal studies on my main instrument (student). I think you have to figure out what you want to achieve, how you will be achieving it (consult a teacher?), what routines you will have, try it out to see how long it takes and then organize your time accordingly. If you are already a musician you will know how to practice effectively so that less time will yield more.