1 - 2 horas
Fusion Drives are _waaay_ too expensive and you get no option of how big you want the SSD-- so why not bolt in my own? And the disk they ship with the thing... oh, if I never have to use a 5400 RPM disk again it'll be too soon.
The Mini is not the easiest thing in the world to get at the guts of-- the main hard drive is easy to replace, but the secondary hard disk requires basically everything to come out of the machine-- hard disk, power supply, all of it. iFixit's kit let me easily do a professional job, and their online guide made it... well, dealing with the guts of a mini ain't never gonna be simple, but iFixit made it no tougher than it had to be.
It's all on the page.