Hi Judy,
" Since I can rely on no frost until Halloween do you think I could start some seedlings and get them to flower as a test? "
Yes, go for it. And you can actually speed up their development by "babying" them with plenty of soluble nutrients and enough spacing between plants that they aren't acting as weeds toward each other. The closer to optimal growing conditions you can provide, the sooner you will get good flowering. I'm not growing Zaharas, but my Zinnia elegans ("regular zinnias") show at least two weeks between well nourished and watered and rather neglected.
ZM
