Thesis defense: 7 days remain
For a conference talk, I pretty much have one point I want to get across, and I have 7 to 15 minutes to do so. If I have anything that requires length, I do a poster and just have to give a short (like 1-2 minutes) and non-technical elevator pitch, and anyone interested will swing by to chat with me about the details. But for a conference talk I have a captive audience ranging from my adviser (who has been following my progress and has probably heard me rehearse) to 'that undergrad who wandered in because rings sounded interesting'.
The audience is a bit similar for a thesis defense, in that, say, a cosmologist might not know much about the rings of Saturn besides 'they look very nice'. Considering I have a cosmologist on my committee*, I need to talk for her as a general 'knows physics and astronomy, but does not know about 35 years of ring research** and does not need to know all of the details'.
But the length means there's a temptation to put all that in, since I'm trying to summarize a 200 page document that took me *cough* years to do. Thankfully, several friends sat me down after the practice talk and said 'you are bogging down in details, cut as much as you can from that and focus on the major points of your research and the background people need to understand that'.
They also suggested labeling the giant picture of Saturn we have in the room I'll be defending in with post-it notes so that people can look at it if I start naming ring regions. Which, hey, if I got it, I might as well use it.
* Rules are you need at least one person outside your field, so I have two planetary scientists, a theorist that models gas disks around stars, and an observational cosmologist. The last two have appointments outside of astronomy as well. (So one is both a Professor of Astronomy and a Professor of Physics, and one is both a Professor of Astronomy and Professor of Applied and Engineering Physics. For that matter, my adviser is the only one who doesn't have a dual appointment -- the other planetary scientist is also a Professor of Mechanical Engineering. Most people get around Cornell's requirement that you have a 'minor member' by a professor with a dual appointment... or an Earth and Atmospheric Science professor if you study rocks or something.
** 1978 is the earliest paper I cite in the dissertation.