Calm corner for kids

Hello,
I have a 6 month, 3 yr and 5 yr boys. I am having a very hard time having my 2 older kids stay in calm corner when they aren't ready to relieve instruction. They try to bite, hurt, pinch, and make a game and laughing to try and get free of wm ans yelling help help and I had to sit there with my 5 year old for almost 40 minutes until I had to use a threat to get him to sit because I had my baby to nurse and my 3 yr needed attention. And his heart still wasn't ready to do his consequence after he sat there to get calm. What does a mom do when this happens? I know it will take time, but it took up my whole morning. Thank you.