I agree about the Fall planting for cold stratification. I think it also depends on your rainfall patterns. You need good moisture for the seeds to germinate. Also, you need to scatter or sow late enough so that the seeds don't germinate until the following Spring. Now this is my advice. Others may feel differently.
Depending on what kind and how much grass there is, it has been my experience that the seeds won't do well in competition with a lot of grass. I've tried that before. I clear at least some patches down to the bare ground so that the seeds can take hold better there.
Because of some of the types of grass we have, it's very difficult for things to compete. I have had success with planting daffodil bulbs to naturalize as well. They come up and bloom in the Spring with no problem before the grasses really take off growing again. Also, wild violets can hold their own fairly well. At least they can here.
