Make sure you keep applying it until the weeds are completely dead. If the neighbors yard has them, they will come back, so you have to work together to finally stop them. Henbit is a winter annual that sprouts from seeds in early fall and grows until the cold stops it. It has a head start on the other plants in the spring. A pre-emergent applied in August will help prevent it from growing.
Violets are very weakly rooted and in many cases pull up easily, if the soil is moist.
They have a thick root that stores nutrients so it will have to be pulled or sprayed repeatedly to kill it. In gardens and large areas of your lawn that are to be re-planted, you can kill these and many other weeds with darkness. Cover the whole area with several layers of newspaper. Wait a week or two and then rototill the whole thing under. Black plastic works well too and can be left in place for a vegetable garden area to help keep down the weeds.