First things first. What do I need?
Obviously you cannot get around the hardware requirements. The list of hardware is short and cheap. Almost no technical skill required. If you can plug a modern TV into a wall, you can get a Raspberry Pi connected.
A fair list of requirements is available here:
https://flightaware.com/adsb/piaware/build
How much time is required?
Using the old method this depended on a few things. How familiar are you with Linux? How many sites do you want to configure for? Are you configuring from scratch? Do you want more than one device configured?
It could take anywhere from an hour to several hours. The uninitiated could spend even a couple of days.
With my method the initial setup might take a little while. But once the basics are done, the first site could be up and running in 5 minutes. Converting a pre-existing Raspberry Pi (once the image has been downloaded), can take as little as 2 minutes.