How long will it take to finalize an hour long HD movie in iMovie on the Mac Mini which has an ATI Radeon 6630m Graphics card

I'm thinking about purchasing a Mac Mini in a few months. If I do buy a Mac Mini, it'll be the 2nd tier one with and ATI Radeon graphics card because I like to do video editing in iMovie. How long does it take on average to finalize/export( a 1 hour long HD(720p or 1080p:please specify) movie in iMovie on the 2011 Mac Mini that has the Radeon 6630m graphics card?