This feels like a trap -- if the experts are so unreliable, and we are going out of our way to be clear about how unclear this forecasting business is (currently, anyway), settling on a number seems premature. If we want to disagree with experts, we should first be able to indicate where they went wrong, and how, and why our method and data will let us do better.

What is the last date at which you think the probability of human level AI is less than 10%?

Sometime after the Singularity. We already have AI that surpasses humans in several areas of human endeavor, such as chess and trivia. What do you define as "human level"? The AIs we have now are like extremely autistic savants, exceptional in some areas where most people are deficient, but deficient to the point of not even trying in the thousands of others. Eventually, there will (in theory) be AIs that are like that with most aspects of human existence, yet remain far inferior in others, and perhaps shortly after that point is reached, AIs will surpass humans in everything.

Trying to predict "when" seems like trying to predict which snowflake will trigger an avalanche. I really don't think it can be done without a time machine or an already operational superintelligent AI to do the analysis for us, but the snow seems to be piling up pretty fast.