Won't abalone be unchewable and stony if you steam for 6 hours?

The last time I went to a seafood restaurant in Sai Kung, we bought fresh abalone from store on ground floor, then took it ourselves to restaurant. Restaurant cooked them in 25 mins, and abalone was tender.

On the other hand, a blogger describes a dish made with abalone that was steamed for a very long time.

The first ingredient to come out was a pair of abalone from Australia which have been steamed with sake for 6 hours.

So what’s the difference between cooking the abalone very quickly and very long – and what about the times I between, e.g. cooking the abalone for an hour?