after you buy it says that if you sell you will get 79% of the price due to agents fee
i've never checked how long is it until it goes back to 97% but if that helps, i bought Zuya at 14/10, and now i will recieve 89%
Minas at 22/9 and i will recieve 94% and Bowyer at 9/9 and he is at 96%.
so i guess it takes about a whole season