I add it to my soil before planting. Even using a quality soil ( Fox Farms ) I have found that by adding lime to it before using keeps my plants from having problems/issues in the middle of flowering that they would normally have when I didnt add it. Such as PH problems etc.. I use Espoma brand ( pic below ) but it comes "pelletized" and I always grind it up in an old blender that I use specifically for this purpose.. But you can easily find and use the dolomatic lime in the huge bags and its also already in the powder for also so no need to grind it.
I use Advance Nutes Ph Down .. its super concentrated .. i use about little less than a cap full to make my tap from 6.8 to around 6.0-6.2 and its like 15 for a bottle