How to make my animations hang on certain keyframes longer than others?

Hello all!

I have a walking cycle animation, however I do not want each keyframe to be played for the same duration. For example, I want keyframe 1 to last 6 frames, keyframe 2 to last 10 frames, etc, etc.

How would I go about doing this? Please tell me I don't have to clone frames on my sprite sheet :l

Thank you for your time!