Sow in pots now and leave them outdoors - not on the windowsill. They may germinate next summer but more probably the following one.

As Bulbaholic rightly said, they may germinate next year or it could be the year after, as it depends on what type they are. There are two types... Fast growing and hypogeal types that have a two stage germination process and so are slower growing.

Another thing to be aware of is that if the mother plant is a hybrid then the seeds probably won't come true.