I suspect the type of meetings you are going to are radically different than I am use to. I would often go on travel and attend two day meetings about once per month. Many individuals gave half to one hour presentations. So how did I manage it. Well most technical people speak in acronyms. And everyone's eyes would gloss over in boredom. In many cases only the presenter knew the meaning of these acronyms. And no one asked what the acronyms meant because that would make them look foolish or uneducated. That is everyone except me. I hate acronyms, so almost every time someone used an acronym when it came to question and answer time, I raised my hand and asked them to define each acronyms they used. As a result I learned things. Most of the others in the audience appreciated this. Their eyes would brighten for a second and they felt like the meeting held meaning.
As far as giving presentations, I always used viewgraphs. In today's world those would be digital presentations such as Powerpoint. I always brought a prop. This is similar to show and tell. The prop directly related to what my presentation was about and I would always explain it in detail and then pass it around the room. No one fell asleep during my presentations. I actually learned to become a good speaker and presenter.
"How do you keep these situations focused without growing frustrated over a long time scale?"
Be prepared. Figure out the questions that are going to be asked and then rehearse your answers.
I once went into a 30 minute presentation that I sense was going to be a difficult one. I prepared around 30 viewgraphs but then I also prepared another 100 viewgraphs for questions that might be asked. My presentation lasted for an hour and a half. I landed up using every one of my viewgraphs. Every time my sponsor asked a question, I pulled out a couple viewgraphs and answered to the best of my ability his question. Beads of sweat trickled down my face.
At the end of the presentation before 100 people, my sponsor said "I want you to know that I am not picking on jimmy m. But he is the only damn person in this room that has answered my questions."