My son is almost 17 months and is very defiant. How do i discipline him at that age?

He will throw the food off of his high chair while looking at me straight in the eyes and then he sits back and puts his hands behind his head and acts like he is is sleeping. I have tried "no" and he just says no back. He only says mama, dada, and no so from what i know he is a little behind on his speech. But he is very smart, he can understand exactly what we say to him. We tried time out but it did not seem to be working, he would do the same thing again when he got out of the time out spot. I do time out continuously and have been for many months. We tried popping his hand gently and explaining to not do that and he hits back. So we stopped that to stop his hitting. I didn't want for him to think hitting was okay. Kinda at a lose, not sure what else there is to try. if you have any suggestions please share :)