回複：請問這裏有沒有J-1豁免拿到，但因時間問題不得以又延長了原來

Yes, it's legal to extend J1 to the maximum of 5 years regardless of having a waiver or not.

If you extend your J1 after waiver approval, a second waiver is required when you try to change to H1b in future or before your I-485 approval. But Chinese Embassay only issues ONE "no object" letter to each person in each J1 period, which means you have to go back to China after J1 or find another way to get the second waiver.

If I were you, I would not think about J1 extension after waiver approval, that makes your waiver approval notice useless.