Preen doesn't last for more than 6 weeks and then it is no longer effective. I would presprout your seeds on damp paper towels in a baggie, transplant into containers until they have a good start. By then the preen may be gone. It doesn't affect plants, only the germination of seed.
Keski

Thanks so much! I am salvaging an old (40+ years) garden spot which has been nelected for about the past 25 years and it was overgrown with brambles, honeysuckle, honey locust, henbit (do I ever hate that stuff!!)and weeds too numerous to count, so when I re-habbed the beds I got carried away with trying to prevent and the weed seeds from sprouting. Thought I'd shot myself down for the season. That time frame will stop me from planting the cool weather crops, but they can wait until fall.