Number of slides for 45 minute defense presentation I have 100 slides but most are light weight with pictures. I am afraid it is too much because I can't get it under 1 hour in my rehearsal. I have noted that some slides take me more time to explain. Any suggestions other than reduce number of slides? Maybe use some kind of timer.
Why are you fixated on the number of slides? What matters is the story you tell, the important messages that people who listen to you will be able to take home after the presentation. Sure, you'd like to say more, but that's not how it works. Don't plan to talk faster, to run through your talk at lighting speed. If the content doesn't fit the time frame, drop some things. You may not want to hear it, but you have to.



Another hint, maybe too late for you, but which I find useful: there are two things which are very interesting to know about yourself as a speaker:


How fast do I usually go? I.e., for a typical presentation, how many slides per minute do I do? This allows you to get a rough idea of timing, for future presentations, even before rehearsing (or allow you to skip rehearsing at all, once you become good at it!).
In real circumstances, am I faster or slower than during rehearsal? This depends somewhat on circumstances (being tired, being excited, etc.) but it is still interesting info. For example, I know that I tend to digress more during real talks than rehearsals, which means when I time myself I know I have to leave some margin. On the other hand, some people talk faster on the stage.


When my students preparer for their first conference talk, I usually ask them to think of the above, and write down their timing. It is useful to prepare later talks, and also their PhD defense!