2 - 4 Stunden
I wanted to add a second internal drive to my 2011 Mini.
Overall it was simple and straight forward using the iFixit guide. It took about 45 minutes to do the whole thing. I ran into a few issues, but if you are competent enough to take it apart you can get it back together again.
There were 3 issues I ran into:
1) The guide lists the bolts that the bottom cover lock onto as being T8 (Step 8), but the T8 bit included in the kit was too small. I had allen wrenches laying around and found one (no idea on size, sorry) that fit and did the job.
2) In step 4 it says to lift the fan off the standoff, but mine was bolted down and had to be unbolted. In doing so this removed the bolt in Step 14 (circled in yellow).
3) There is no guide on reassembling the Mini (I really dislike "lazy" guides that end with "just reverse the process to reassemble") and I ran into issues getting the power supply reinstalled. There are guide pins on it's side and rear (front of Mini) when need to line up properly. The rear pin was my trouble as sliding it in with the Mini upside down left it too low to slot in. I found having the Mini right side up, small fingers, and a good light were the keys to getting it back in properly.