When to plant annuals?
Annuals should be planted after all danger of frost has past. This date will be different, deponding on where you live. Make sure you find out what (zone) you are in, so that you know when to plant.
They can be directly sown where you want them, although keep in mind, planting this way you may have surprises from seeds wandering.
Annuals can be planted earlier inside. as long as you have the right conditions.(check growing from seed, for more info). This method works well for those gardeners that like to keep things organized in the gearden.
If you have a store bought package, it may have an approxiamate time to sow inside, before you plan on putting them outside. Not all packages do. It is best to do some research on what you are planting, as most packages don't have much info, and the time to start varies with different flowers.