I use Quick Look to go through photos quickly, and I thought the slideshow feature could come in handy if I can change the duration of each photos shown.
I tried sameer's answer, but it doesn't seem to work any more with Mavericks. Another thing I noticed was that Quick Look's slideshow duration was 4s, while the mainDuration value of JustASlide is set at 3s, which makes me wonder if this is the right settings file to begin with.
On a side note, Preview has its own slideshow feature as well, but I can't change any of its settings either.
If there's any way I can change the settings of these slideshows, I'd really appreciate it!