It depends on where you live, when you purchased the bulbs and if they have been refrigerated or not. If it is spring where you live now and you just bought the bulbs, they probably have been refrigerated so you would need to plant them now. If you live in a place where the weather is cold in the winter, you can order bulbs now that will be delivered in the fall and you plant them in the fall before the freeze. The cold weather will set them up for spring. If you live someplace warm, like Southern California or the Gulf coast where winter temps are mild, you have to dig and refrigerate your bulbs in the winter. In cold climates you can leave them in the ground.
I live in Central Ca. and our tulips are blooming now. Actually bulbs can be planted anytime but maynot bloom until the second year. I planted some irises in the summer 2 years ago and though they came up last Spring this is the first season they are blooming :)