From a physiological point of view, chronic and acute thermal stress are two totally different beasts with two totally different solutions. Many coldwater intertidal animals are very good at dealing with acute thermal stress which makes them popular within the hobby, research and aquaculture. They're very hardy, but that doesn't mean any temp is good.
Some mussels regularly reach temperatures of above 120 degrees. Different species of "margarita" snails regularly see temps in the 90s. Tigriopus are documented to survive to at least 100 degrees and can stand being frozen solid. Still, there are measurable signs of acute stress well before the animals reach those temps and even at sustained temps much lower than that survival drops precipitously. That's the norm for intertidal animals. Similar work has been done for sea stars and all sorts of mollusks. Even for animals with such high tolerance for acute stress, thermal stress is such an important limit in geographic distribution that you can predict with surprising accuracy where they will and won't occur based on the local temp profile.