Yes you can certainly add fish well before 9 months. I applaud your patience in waiting before adding the corals. This is a good thing.
Inverts are sensitive, so I woild wait until your tank cycles, about 4-6 weeks, before adding them.
After the cycle, you can add LR slowly at any time without a cycle, as long as you do it SLOWLY. When adding LR to a fully mature tank, you can add a piece at a time, of cured rock, without too much fear of a recycle. I added 125 lbs of LR to my 125 gal tank this way. I simply added a 2-5 lb piece at a time. Once I added a 20 lb rock and all was well.
So, I would put in your DSB, your LR, your water and let her go. Keep testing till you are sure the cycle has ended, then add your inverts and cleaner crew. (Keep in mind, the cycle time is different for each application).
After that, you can add your LR a piece at a time. Then add fish (if you are going to have fish in your reef), and lastly, after the tank is well mature (6-9 months) add your corals one at a time.
Whala! Reef tank!
Like everything else, this is just my (successful
) way of setting up a reef. There are as many opinions as there are people. But on most of the basics we all agree. The most important asset in this hobby is patience.
HTH
Hermit