2 - 4 hours
my hard drive was filling up quickly on my Mac Mini. i decided to install a 240GB SSD for system and applications, and use the existing 500GB HDD strictly for storing my photos.
Everything went great! Disassembly was way easier than i expected it to be. The cable that came with the dual drive kit fit perfectly. it was also well worth the extra $10 to get the tool kit and spudger.
Make sure the SATA cables are connected properly to the motherboard. one of mine popped back up a little bit after assembly. (it was actually the factory one.)