Glyphosate breaks down pretty quickly. One of the debates about it is how quickly this actually happens, namely in the context of over-application, but in any

Glyphosate breaks down pretty quickly. One of the debates about it is how quickly this actually happens, namely in the context of over-application, but in any case it's pretty quick. The low environmental persistence is one of the major selling points. After a couple months, chances are even a very sensitive assay wouldn't be able to detect it in your lawn. As a one-off use, I don't think there's even a marginally compelling argument that it's dangerous.