I think this is probably one of the most over thunk things in brewing. I've read about hopping til I'm blue in the face. I've never ruined a beer by hopping it badly, in very many attempts.
I think some of what commercial breweries do is governed by ease of production, and the equipment they have. And some is about marketing. So, there are lots of DDH beers in bars and shops now. Double dry hopped. During fermentation for biotransformation effects which transform the flavours, and post fermentation to get hop oils into the beer just before packaging, to minimize losses. Other breweries just do one or the other.
There isn't a right or wrong. You can add hops at any stage of the brewing process and people do. In the mash, in the kettle pre boil, start of boil, mid boil, end of boil, as it's cooling. In the FV at any stage. Some brewers simply make a hop tea and that's the entire hopping.
The duration of dry hopping varies enormously too. Consensus is that a dry hop needs 24 hours + but most people go longer. 2 to 3 days is ample, longer does not increase aroma, and may reduce it. 1 to 2 days is probably optimum I suspect.
But it's not hyper critical, the differences will be marginal and hard to detect in my experience. The hoppiness of beers is mostly affected by the quantity of hops used and the varieties used. On a tour of Cloudwater the head brewer told us that the beer in production was getting a 25g per litre dry hop with Citra, Mosaic etc, leaving little room for nuance or doubt! I've tasted those beers and they are very hoppy!