The person may sit in fully supported seating for 2 to 3 hours per day. The hours will need to be divided into several sessions with different things to do and constant cuing.
If partially supported seating, without head support, is tried, the time should be limited to a few minutes to avoid fatigue. The consequences of over-fatigue can last for several hours of troublesome, agitated behavior.
The pull of gravity may start a slow slide out of a vertical chair that may not be noticed by the person and they will not be able to make the adjustments necessary to overcome the effects of gravity.