If all goes well, Caroline, two growing seasons and one winter should do the trick.
A wheat seed is a good analogy. I have to say, martagon seeds that I've grown with 3 month cycles inside the house are usually even smaller! I suspect they are a little bigger when they are grown outside, where the environment is more amenable. Consequently, the one seedling leaf that will emerge in the second growing season will be larger, too. For me so far, the largest hypogeal germinating lily seed bulbs have been L. monadelphum and L. polyphyllum.
