I sprayed some weeds in the front yard last week with "broadleaf weed
killer". They are now wilty, but not dead.

What to do now?

I'm generally one not to use weed killers, but this patch of yard is so
dense with weeds that I simply threw up my hands and said, "kill them
now". I mixed from concentrate, and got the rate right, but wonder if
maybe the concentrate is "stale", since it's a year or two old now??

so, respray with fresh killer?
wait another week and see if the weeds finally go brown and die?
what?