I have a large number of photos that I want to turn into slide show and combine them with a few clips. My question is how do I set the time/duration for all photos to be exactly the same like 3 secs?
You can set the internal preferences to default to whatever length slide you want.
To get to the internal preferences, click Option, then hold the shift key down and choose Preferences. You'll see a tab marked Internal.
Search for the word Still. I think the default value is 50000. Change the 5 to a 3 so that he number reads 30000 and your stills will automatically come in at 3 seconds long each.