if you buy concentrate, you mix something like 1tbsp to 1 gallon of water and add a few drops of dish soap, then spray onto plant. i buy the pre mixed ready to use green light rose defense, it has worked for me.
i've noticed that i get a little leaf burn sometimes, but the plants also get a good growth spurt from the neem oil. if you mix it too strong it will fry your plants. it will probably take a couple weeks to get rid of the mites, they will be gone by the time you harvest. i've never had a problem with mites because i use neem from the beginning of veg. as a preventative. i use it up to 1 week before harvest. i spray the soil with it too.