I believed to remember that it involved setting some envvar. (Actually I did check for that in the manpage but did not find anything. But I did not go through the options, because I was so certain it involved a envvar.)
Well actually it does not work with git from the master branch:git rebase -i --ignore-date a7a86feerror: unknown option `ignore-date'This seams to be a bug however: in the manpage this option actually is listed.
I have tried it before posting.. Except for I haven't done it interactively, maybe that's the trick? Also, have you tried the --committer-date-is-author-date alias? Maybe the --ignore-date was introduced in later version, I have no idea.