I see you have already booked some A-list personalities. Have you tried tapping any of the regular Forum contributors, asking "Hey, would you be willing to talk about . . . . "? Or, maybe some Forum member would nominate a potential presenter here in this thread.
It always depends on what you want to convey. Some talks get boring after 15mins but others are still worth listening to after 50+mins.
Talk to a mirror or better still record your self and watch it back. Hearing your self will give you a good indication of how good your talk is. (don’t force a particular length if you have the freedom to choose. Some length will show itself naturally after a bit of training.)
@ChrisGammell could probably give more insight. I don’t know what the format of the thing will be. Will this be a ‘one room’ thing or will they be offering a couple venues and giving choices? If that’s the case you might need to come up with an hour or perhaps share time with someone giving a similar talk.
Something to consider is is a morning/day for training for a new user. I am a heavy Altium user and have been keeping an eye on Kicad but it is very expensive (in time) to learn the workflow. It would be efficient to have a day to see the workflow (create symbol, map 3d models, library management, schematic entry, pcb layout, documentation prep, etc). from someone who is skilled who could answer questions.
I am hopeful that Shawn Hymel will update/redo his step-by-step 10 part tutorial series for KiCad 4.7 to be applicable to 5.1. I used his video series for my first PCB and everything went very smoothly for me. Without his videos I think it would have been more of an uphill battle for me.
Try Dr. Peter Dalmaris’s “KiCad Like a Pro 2nd edition”. He covers KiCad 5.0 using a Linux OS and his “recipes” are great. It’s not free but it doesn’t cost that much either, I paid US$9.99.
–Larry