When using vinegar to kill weeds it does work but usually it takes a day or 2 to see the weeds completely die off.
You can also mix the vinegar with some salt and dawn dish soap which usually helps kill the weeds much faster than just the vinegar itself.
When using the vinegar, salt and dawn dish soap together the weeds begin dying off within the same day and within a few days the weeds are usually completely dead.
I like using the above solution as a natural weed killer because it's not harmful or toxic to pets or humans.
The natural weed killer of vinegar, salt and dawn dish soap is safer and in my opinion more effective than Roundup or other commercially made weed killers.