I use 30% sulfuric acid and had them germinate at 15 minutes. I may increase that to 20 minutes, but 3 hours seems way excessive.
It has been my experience that most Rubus seeds only last a short time. I store mine in the berry itself i.e. I don’t clean the fruit of seeds till I’m ready to start them. You can store Rubus long term by freezing, must be dry!
So most seeds you buy will be dead. The best way to practice is take some fresh brambles and remove seed, use those right away. If you don’t have any, go buy some fresh berries. Driscoll has about 20 raspberry cultivars you cannot buy, they developed them for their farms. I just saw about 10 new raspberry patents and 10 new blackberry patents by them. So growing out seed, might not produce mother plant, but may result in a very good berry from gene lines we cannot purchase.
That should be Scarification, they do need stratification too.