When my kids were playing in the playground, I always give them an advanced "warning" on how long they can play. The warning is typically "you have 5 more minutes, or you have two mintues." It works most of the time.
Before commanding him to do a task, set up a reasonable time table. When he is in the middle of gaming, tell him that he can play either 30 minutes more or can play untill a set time (8:45PM, 9:10 PM), then he has to do the task. When the time is up, remind him about the time if he has yet to stop playing. If the reminder is ignored repeatedly, there should be an hardstop, regardless of what he is doing, he will have to do the task. Do not do the task for him. If his job is take out trash, remind him only, do not take out the trash for him. If it is his job to set up the dinner table, no dinner untill the table is set. Repeat daily. It takes patience.
