My friend is a horticulturist. He said the half life of most weed killers is 3 weeks. So if I wait 6-8 weeks it should be ok.
You need to read about "killer compost". These toxic weed killers that are "supposed" to break down into inert substances are lasting for YEARS. They are being sprayed in hay fields, eaten by animals, pooped out and then composted for YEARS and then are still able to kill a persons ENTIRE garden in a single season. That person buys horse manure or compost and thinks they are being natural to find that their garden gets sicker and sicker.
I have read several stories about people losing their entire property and having the soil become so contaminated that their properties are sterile and will grow nothing. The only solution is to bring in machines and strip the top soil down and then try to build it back up with green manure.
If the label says it's toxic to waterways and frogs then you know it should NEVER be used anywhere. Period.
I now have a closed system and bring in nothing from the outside except perlite and locally grown wheat straw. My soil is a work in progress.
In the Spring allow your lawn to grow high and mow on the highest setting. This will allow the root structure to become strong and it will weather drought better. Lawns are the top users/wasters of water. If you are in a drought, let the thing die. If you allow natural plants (what many call weeds) to grow it most likely will weather dry spells much better than turf grass that needs coddled more than an orchid farm!!
I know that I'm coming off a bit snotty, I prefer the term passionate. This issue isn't going away and people just can't believe that these products could possibly be harmful. I was talking to someone who blew me off and said "If it were harmful to the environment or to people then they wouldn't sell it in stores." Wow. They had very thick rose colored glasses on. But that's how many people think.
My Husband's Uncle used to try to give us veggies from his garden. I wouldn't take them. He sprays Seven about every 5 days or so for the entire season on his entire garden and property. No mask, no gloves, no long sleeves. It's just scary. His garage looks like a chemical factory. If you can't drink it, don't spray it on my food!