Rhubarb crowns (bought) go into a well prepared bed in March and any flowers taken off then, you are looking to the following year for the stems.
From seed they will take a lot longer to harvest stems and I would put them in now.
We used plenty of manure or good compost and bone meal as well, they are hungry plants. A bit of shelter is good say near a wall or fence, they want to be around three feet apart.
We had long rows of the plants so forced some each year by putting straw round the crown and a bucket over the top, it was usually the first garden fruit we had hence the many rhubarb recipes and the annual glut of rhubarb and custard with school meals, I loved it a lot did not.