Keep on your counter at room temperature. You have to check everyday if they are ripe as these guys tend to go from not ripe to overripe overnight. They are ripe when they are a bit soft when pressing them and when the little wood bit at the top detached itself easily.
How to prepare
Cut them in two, remove the stone (and put it in a pot with soil, pointy bit up and just covered with a couple of mm of soil :), scoop out the flesh. You can eat it like this with a bit of salt and pepper, or you can put it in a salad. They also go very well with shrimps if you like these.
Note that the weight and number of pieces are approximate.