I can remember the 1080 launch.
there, I just tracked pricing as a function of available inventory — if the pricing remained at or above MSRP, the demand wasn’t being met. Once I started to see retail pricing dip below MSRP, I figured we had finally met demand and had seen the supply chain catch up.
There was never any word about volume shipments, although after the fact you could probably make some educated guesses based on what popped up in things like Steam Hardware Surveys.
Using the MSRP metric, the 1080 launched May 26, 2016. It wasn’t until August 14th that I started tracking cards being sold regularly at MSRP (there were still inventory issues with specific SKUs)
1080 launch is probably closer to the 3080 than the 2080 was - it also brought in a new memory standard and was a pretty big leap over its predecessors.
So yeah, months before I would expect reliable inventory, and maybe longer if you are waiting for a specific model (Strix, etc).