Stop Motion Video - Frame rates, FPS and Duration

Hello everyone. I have taken over 800 photos for a stop-motion video I am creating, I have now put all the photos into Premiere Pro (CS5.5) and want some advice on understanding frame rates, fps and duration.

From my understanding, if I make all the photos a duration of 0.04 seconds - it should export a smooth high quality video at 25 fps.

However, there are some 'scenes' in my video which I wish to play at a faster rate of 0.02, as during playback, the speed works much better with the voiceover I have paired with it.

Can I make some photos have a duration of 0.04 secs and some photos at 0.02 seconds, and it still export at a high quality smooth video? Or would i be best to put all photos at a 0.02 duration, and use the 'two's' technique of putting two of the same frames at 0.02 secs to make 0.04 seconds?

Also, what would happen if I made some photos a duration of 0.03 seconds - would the video stutter when exported?

Please bare with me as I am new this technical form of stop-motion! I hope someone can assist me.

Thank you so much in advance.