How do I change the transition speed of a slideshow gallery?

I want to speed up the fade transitions between images in a typical gallery, faster than what's available as a preset. How do I do this?

This link, with its javascript hack, I found helpful for cover pages, where I could really tweak the transition to the millisecond:

http://answers.squarespace.com/questions/55637/how-can-i-change-the-speed-of-a-cover-page-slide-show

Anything similar for regular galleries? Thanks.

When in edit mode for a page (not style editor), click on the edit button at the top of the gallery block. This will take you to a pop up that allows you to modify this option on a slider under the design options.

This isnt an option on Foster template