Hope these help (when looking at the first pic click on previous to see the next one, for some reason they are backwards in order from the gallery)
When you set up the gallery you can choose which order for the pictures to be presented. Ascending or decending. You can also choose wheather to order them by date, title, most viewed, etc.
If you choose by date, I believe it uses the time stamp in the exif data to determine the time the picture was taken.
If you want to show a chronology, sort by title and ascending, titling the pics in the order you want them to appear. Using a 5 digit numbering sequence is best for 100 pics or less. Like so: pic00001.jpg, pic00002.jpg, etc.
This is necessary because the directory structure will take pic1, pic2 and place them in order but when you get to pic10 it will place it in front of pic2 because 1 comes before 2. Hope that made sense.
You can edit the gallery any time after you set it up including titles.