Once you put the salt on the weeds it can take up to 10 days for the salt to kill the weeds.
It also depends on the weather conditions but a minimum of 10 days is what it takes for salt to kill weeds.
You can also dawn dish soap and vinegar and mix it together in a sprayer or spray bottle and the dawn dish soap and vinegar will kill the weeds within a few days.
I find the vinegar and dish soap more effective and faster at killing the weeds than just salt.
You can also add some salt to the dish soap and vinegar to make it more effective.