2 - 4 horas
I wanted to install a 128GB SSD alongside the 750GB spinning disk to make my mini faster without having to sacrifice space or a huge amount of money.
It was very easy to take it apart. The only difference with the guide I found, was that my fan was bolted down with an extra screw. The hard part was getting it back together again. The logicboard wasn't flush with the backside and I couldn't get the original harddrive properly aligned with the holes in the antenna plate. I solved this eventually by swapping it with the SSD and by removing the mounting screws on the side of the SSD. The problem with the flush logicboard was then also solved.
Taking stuff apart is always easier than putting it back together, so pay real good attention when you're taking it apart.
Also, I'd like to have ordered just the SATA cable and the stick thing. Not the screwdrivers. I had those.