Perhaps 20 minutes is soon, but if you think that he was too stressed and you were upset about it too, perhaps this method isn't the right one for you, but the method did work for us and I am a great fan, I know though that it doesn't work for everyone so go with your instincts. Have you seen the post about different sleep training techniques? Have a read, but I do think that WI-WO is right for his age so I would give it another go, but ensure that his routine is consistent and you have the right frame of mind, I could have done it months earlier, I just wasn't determined enough IYKWIM, so probs would have given up too soon.
The problem is, if we try too many different things, half heartedly, then give up and try something else, then we will just confuse them. We have to be consistent and they will catch on.
Saying that, you know you LO and I am sure that you know what is best. Whatever you decide we are here to help you and answer your questions if we can and above all, support you whenever we can. Good luck.