2005 mini, how many hours should it take to replace a head gasket? And, is it any more difficult than normal to do this job?

 

get a Bentley manual. make damn sure of your timing marks and chain.

 

I'm in the middle of doing this as we speak.

If everything goes smoothly and you have every gasket, part, and tool that you need, you should be able to do it in a day, working morning into the night. Maybe less. Just be sure to clean the head and block decks really well. also, like newb said, get the Bentley manual.

I would put all hardware that you take off into separate ziplock bags and label them (motor mount, intake manifold, etc).

As for the timing mark, even if you don't mark it, worst case you pull off the timing cover and align the chain to the arrows on the sprockets.