What's the best art pipeline for 2D animated sprites?

I’ve read many questions and answers on the subject but none scraped an aspect that is vital for my project.
I’ve got sprites that have been animated with different tools (GIMP, Photoshop, Flash) and some of them have different delays between each frame.
I would like to import the animations keeping the delays of the different frames so that I do not have to rebuild them all by hand each time I reimport the animation.
Has anyone accomplished something similar?

Just google how to implement frame based sprite animations into unity3D. You can set the speed of the animations in the same window. To keep the delays between the animations increase the time distance between the two frames. It’s not hard to do and it all can be done without touching a single line of code.