SWIM is trying to grow some right now. A friend grew from the same seeds as SWIM is growing and he said they take ages to start growing. It took like a month for my friend to notice anything popping out of the earth. Many seeds did not grow, some did. He just put it on little pots with earth and sprayed some water once in a while. You dont want to flood the whole thing, remember mimosa comes from dry areas, but also dont leave it too dry as for the seeds to start growing they do need a bit of water..
SWIM has another friend that might know more, also about the later parts of the process when it got a bit bigger, but he hasnt come online for a while.. Any info I find I will try to post back