Excuse my logic if it were incorrect about factual gardening related knowledge (i would love to be corrected) but it would be possible to grow the bulbs earlier if you were planning on only keeping them inside the greenhouse the whole time, as with a greenhouse, the advantage lies in the fact that you can maintain a set climate? So technically this means you can make it whatever season you really wanted, apart from the fact that the real seasons that are occuring naturally may be limiting or increasing the amount of sunlight that is provided directly to your plants.