It appears the default duration for all photos is 5 secs when imported. The slider is super easy to use to change the duration manually for each photo - is there an option to change the default import duration for each photo?
Correct, stills and title cards have a duration of 5 seconds, which you can trim down (or duplicate the clip to extend the duration).
There isn't an option for changing the default duration, but it's a great idea! How do you envision that working -- would you like to enter a number of seconds (or frames)? Use a slider?
Community Manager for Premiere Clip