After the starts are planted in the system, about 5-10 minutes a day. That includes those days with a pH and water level check and adding a capful of h2o2. Add a few minutes for updating the journals as I try and keep the entries very detailed.
Early in the hobby I often found myself wanting to do more, but the systems are so easy maintenance I would have to wander off and do something else. ;(
I am sure I will expend many more hours once I begin working an NFT system in the near future.