1 sec after...no really, you dont have to wait. You could even spread your seed first and spray right over the top of it before it germinates. Gly deactivates with soil contact.
I know one of the active ingredients in crossbow, triclopyr, has herbicidal residual acticity with a half life of 6 weeks. Always consult your label, though crossbow may not say much because its not really for crop areas.