Person 1: "Hey"
Person 2: "Cold these days huh?"
Person 1: "I might put on a jacket.. yup... you were right..."
Person 1: "I forgot to file the report! Ms. Johnson is going to kill me!"
Person 2: "OH SHIT. YOU ARE SCREWED"
Person 1: "I am SO FIRED. You were right! I am an idiot!"
The improv purist in me says that both approaches are fine. In fact, the first one may feel more organic and less dependent on a "high energy" gimmick to start a show. I think it's clear to see why an audience will be more entertained with that second hot start. But then I begin to wonder if it's too formulaic to come out with a big emotion every time, and I hate shows where I know what's going to happen before it even starts. Longform improv should be a surprise at every show, it's what drives the thrill of it all.
But I think a "hot start" can be more than just coming out with a big emotion. I think "hot start" could be expanded to just mean have an "engaging" start. For example, I think even the first example (slow build) from above could be converted to a hot start without reverting to yelling. For example:
Slow Build #2:
Person 1: "Hey" [tense pause, stares intensely at Person 2]
Person 2: "Cold these..." [break the stare, begins to cry] "days... huh?"
Person 1: "I might put on a jacket..." [pauses, regret begins to seep in] "you were right..."
Obviously this new version requires a lot of commitment and a good amount of acting skill, but if done well, I'd say it would be a very engaging beginning and any audience would be sucked in. So we don't have to always rely on screaming and cursing to suck in an audience, we can do it with just pure commitment as well. Knowing this, it really expands on the idea of all the different kind of "hot starts" we can have.
In summary I think the beginning of a show is so important, especially for a non-improv audience. If you don't have their attention after the first 2-3 minutes, it will be hard to gain it later. So I recommend try starting your show with "hot starts", filled with energy, commitment, and strong points of view. Or you can just curse and yell a lot... something i do way too much...