The personal benefit of moving with the effects of gravity is being able to sit up with full head and trunk support for 2 to 3 hours a day.
The need to be upright is rarely satisfied by spending the whole time being passive, i.e. being fed or taken care of. Data is needed to establish the percentage of time up that needs to include active engagement in pleasant sensations. To start, I would suggest 50%. Sensory stimulation would ideally occur mid-morning and mid-afternoon.