2 - 4 horas
New Mac Mini - adding and aftermarket 8Gb and an SSD to make this my primary business machine.
All good SSD fitted better on the 'upper' layer; tried swapping them initially then went back to putting the spinning disk in the original lower layer and the SSD into the upper slot.
Read all of the instructions! Getting the main board out of the enclosure takes some commitment. Once out it all makes sense.