It can take20-60 minutes depending on the tools you have and way you install it. Gonna take longer if you solder the wires instead of using male/female connectors (can't remember their proper names for the life of me). But essentially if your adapter from the previous unit fits your new unit, it's just plug n play. If not, grab a universal adapter from super cheap auto. If they don;t have one for your car (like me) then it's down to soldering/connectors. I used male and female connectors.
This is from me doing it in my CC
1. Unscrew and pull off the face plate
2. Unscrew the hinges of the head unit that is already installed in your car (and take the hinges off the unit itself)
3. Screw the hinges onto the new headunit
4. Cut off (with pliers or similar) each wire connecting to the adaptor.
5. Strip about 1-1.5cm of the wire with the pliers
6. Twist the stripped wire around and put each stripped wire into a male/female connector and clamp it shut tight with the pliers.
7. Do steps 4-6 with the wires from the new headunit, and put either a male/female connector on the ends (if you used male for the original wires, use female for the headunit, and vice versa)
8. Clamp those connectors tight again.
9. Plug the male/female connectors together and use some duct tape to insulate + keep all the wiring together
10. Screw the headunit back into the car
11. Screw the face plate back on.
Done.
If it sounds confusing, I apologise, it's a lot easier when you actually do it. Each step takes 5mins max. And yes it's kind of a tacky way of doing it, but it's cheap, it's easy and it works. And who's going to see the wiring anyway?
And make sure before you bolt the headunit back in that you test it, don't want to unscrew it all again if something's wrong.