Pay no mind to the people who tell you that you can't spray your flowers. Guess what happens to flowers grown outside...they get wet when it rains. What you have to do is allow your plant(s) to thoroughly dry prior to placing them back in your grow space to prevent powdery mold and bud rot. I usually just put 2 fans on each plant after a good hosing down and after about 10-15 minutes in front of the fans, they're dry as can be and ready to be lovingly placed back into my grow tent. Another reason you don't want to spray your plants and put them back under your lights while they're wet is that it could roast your plants...always make sure they're dry before you put them back under the lights.
this advice is not only bad, but contradictory.
getting wet with water and getting wet with an oil like neem oil are different beasts. it is why plants can get rained on in the sun and not burn, and also why you should spray your plants with neem in indirect sunlight, such as when the sun is setting. or indoors, at lights off.
as for spraying in flower, it is questionable practice to spray with even neem past 4-5 weeks. but one thing that can always be done that makes life hell for the mites is a spraying with water. mites breed much slower when it is wet and cool, and much faster when it's hot and dry. you can even knock a lot of mites right off the plant with a decent stream of water.*
it is always good practice to dry them off before they go back into the lights, especially when budding, as jonny said.
for the plants in veg, there are plenty of good products like neem oil or azamax, just spray as they suggest and let the plant dry off before going back under any lights. once you've got damage free new growth, you can even get rid of damaged old growth.*
best to always spray preventatively even when you don't have mites. you don't want to wait until you have them.