Well, I cant give any working code atm, but I can point you in the right direction - a few snippets to help you with some of the algorithms.
you'll want a def that cycles through the images, and that times the duration shown. Now, for cycling through 9/10 images, first, I recommend you use an array and loop to create and store the images it's incredibly smaller and easier to handle:
@imgs = 
for i in 0...N
@imgs[i].bitmap = RPG::Cache.picture("img" + (i + 1))
@imgs[i].x = 0
Replace N with however many images you want.
You'll want an incrementor variable, place it somewhere in main or initialize:
@i = 0
And when it comes to cycling a new image, you'll want something along the lines of:
if Graphics.frame_count % 80 == 0 # occurs every 80 frames
@i += 1 # increment the var
show_image(@imgs[(@i % N)] )
# whatever you use to show the image, make sure it's image "(@i % N)" of the @imgs array.
# where @i is the incrementor, % is modulous, and N is the number of images,
# you can use @imgs.size for N here
Hope that makes sense, by the way.80 frames is 1.3 seconds.