Once they focus on getting done, you will be hard pressed to take their project away from them. Most people stubbornly resist stopping until they have used all and can become combative if a project is removed forcefully. Threats of missing a meal may have no effect on them.
Sustained attention to all is often maintained for 30 to 60 minutes.
A schedule of activities that would prevent troublesome behavior probably requires 3 or 4 hours a day. Affirmative activities can be done in groups of 8 or 10 people functioning in ACL 3.8 and above.