The most common class length at most conferences and conventions is ninety minutes. Whether you call it a workshop, a session, a breakout or a class, that's not a lot of time to cover a subject in much depth. By the time everyone gets settled and you make it through the instructor and workshop introduction, you're 10 minutes into your hour-and-a-half. There's still a lot to cover. Some presenters believe in the "speed lecture" method. I've been a victim in these type of classes where the instructor talks as fast as they possible can while flipping through slides at the speed of light. I'm a note-taker, so I've probably shut down about 30 minutes in out of sheer frustration. I wonder if the instructor's goal was to shower us with knowledge hoping some of it would stick. Most likely some did, but I bet it wasn't what he or she had planned.
Instead, because as an adult I want my learning to be meaningful, workshops where the facilitator focuses on just a few key elements are more likely to work with me. I also do better when there is a variety of methods used to present and expand those key elements. I'm a visual learner, so I need images and examples. I like handouts to take with me and lots of references for learning more about the subject. I've noticed that a lot of piano technicians are kinesthetic learners. Lectures (including PowerPoint-based) and videos are not nearly as effective as actually touching something. Demonstrations are good, especially if you are able to pass parts, tools or jigs around for participants to see and hold. Pick out volunteers to help you, or ask the class to help as you review the steps of a particular process. If you are the last session of the day, it's even more important to get people moving just to keeps their brains awake.
For the smaller group of people who learn well from lecture-style presentations, articulate everything you demonstrate or share visually. Refer them to online videos and provide written handouts. They usually like to participate in discussions, so you can rely on them to help keep the group involved.
I was a CPR instructor for many years. I struggled enough with the idea of feeling like I had prepared people to perform CPR adequately at the end of a six hour class, but when asked to do a ninety-minute "talk," I didn't know where to start at first. Then I realized that that was the key. Where to start. So I figured out that in 1-1/2 hours, using some demonstration and a little hands-on practice, my group could learn the beginning steps well enough to make sure someone got the help they needed. Maybe they didn't know how to do CPR at the end of the talk, but they knew enough to check someone in trouble and call for the right help. Some were also motivated to go on and take a class for certification. That's the key. Start at the beginning and give your audience enough to help them feel confident that they learned something new and motivated to learn more.