Yes, that is what the NBER does, although 3 months is only a basic rule of thumb. They will take any amount of time they deem necessary to analyze and draw conclusions on the overall economic condition.
So yes, we won't know the recession is over until it's well over.
Anything beforehand is only a best guess at the future to come.
About the only general consensus among talking heads right now is that we are in for a complicated recovery. No real consensus as to how or when the recession will end. However, I wouldn't be surprised if, a year or two from now, we're still here asking that very same question....