Z.M.
Right now your son is getting a big reward for not falling asleep on his own-- you in the room, and your undivided attention. I suggest you tell him he needs to stay in bed and go to sleep, then walk out of the room and shut the door. Park your chair outside the door, and if you hear him get up, go in, and calmly put him back in bed-- no talking, no scolding-- just put him back. Then leave again. It should only take a night or two before he gets it. It's also possible he's just not sleepy at that time, and you may have to move his badtime back (ug-- I hate it when I realize that!)
Good luck!