I voted up for a comment and realized that it wasn't in fact such a great comment. I am not able to cancel my vote as I can do for questions or answers : "click again to undo" don't work.

Is it just impossible, is there some timeout impeding you to change your mind every 10s or is it a bug in my browser ?

I did not find an answer in the faq or the meta... Edit : should have looked on the other meta-sites.