No worries! If your system ends up being phosphate bound then it will likely suck up whatever you add within 24 hours. It may take several days of testing and adding to get some to appear. While this is happening you should start seeing your NO3 levels lowering. (These are indicators that the system is PO4 limited, and the bacteria are "waiting" on it so they can consume NO3 and surplus carbon). I'd test your NO3 and PO4 daily while you do this. Have some Potassium Nitrate handy incase your NO3 drop to zero, you may have to make an addition or two. You probably won't but it is better to be prepared.
After you get some phosphate to appear on your test kit 24 hours after dosing I would stop additions of PO4 and wait. Continue testing and try and balance your NOPOx additions now so that the tank balances. Or slowly consumes NO3 and PO4, plan to increase feeding to balance the system. Use your KNO3 and NeoPhos for emergencies. Once you know your system is no longer PO4 limited you can most likely let your PO4 creep back to undetectable, but, you want to make sure your nutrients don't get driven down low and another carbon source surplus builds up
You should see noticable improvement in the corals fairly rapidly once there is phosphate available. (Even in the beginning when your tests are coming up zero, you will see changes). This isn't however a "free ride". Once nutrients become available to both your bacteria, and to your inhabitants, it is also available to microalgaes, so be prepared! Beef up your clean up crew, so you can head any outbreak off before it gets away. Your tank can and will support more life with nutrients in the system. Take things slow, remember even when the PO4 is undetectable while you are adding it, you did add it, and it is available. So don't freak out and add a whole bunch. Better to go very slow. Dealing with 0.01ppm of PO4 is a very small quantity!
Feel free to ask me any questions, if I don't know the answer I will try and find it for you. Like I said there isn't a whole lot of information regarding PO4 dosing.