The expected impact of waiting to sell will diminish as time goes on, because you are liable to change your values or, more probably, your views about what and how best to prioritize. This is especially true if you have a track record of changing your mind about things (like most of us). While the expected impact of waiting is, say, the value of two kidneys, conditional on not changing your mind, this same impact will be equal to the value of one kidney, or less, if you have a 50% chance or more of changing your mind. So I guess your comment is valid only if you are very confident that you will not change your mind about donating a kidney between now and the estimated time when you can sell it.
The expected impact of waiting to sell will diminish as time goes on, because you are liable to change your values or, more probably, your views about what and how best to prioritize. This is especially true if you have a track record of changing your mind about things (like most of us). While the expected impact of waiting is, say, the value of two kidneys, conditional on not changing your mind, this same impact will be equal to the value of one kidney, or less, if you have a 50% chance or more of changing your mind. So I guess your comment is valid only if you are very confident that you will not change your mind about donating a kidney between now and the estimated time when you can sell it.