I did a destiny hair render this weekend with 5 actors and lots of props with realistic sky, skylight, and indirect lighting.
It took 2 hours to render at 300 dpi, 4 hours with best anti-alias added on. With the hair turned off it was not significantly faster. So, it isn't a bug with the hair per se, but the hair has transparency which often is demanding on renders.
a)What dpi are you asking for?
b)What are the shader settings on the hair? Is the transparency properly in the alpha subshader? The transparency channel below should be set to "none". I once set it to some value and DISASTER! The machine really choked.
If this is a still, there might be a workaround of doing a bald render, then adding the hair done separately (assuming it renders in a smaller, less taxing scene).