It can be a few hours worth of work, or more, depending. You have to recover the refrigerant, do the change-out, pressure test for least 30min, pull a vacuum (least 30min usually), then weigh in the charge. This isn't something I recommend the average DIY try to do. You need epa certification to legally handle refrigerant. You need a recovery machine. Oxy-acetalyne torch with brazing rods. Tank of dry nitrogen. Vacuum pump. Refrigerant scale.
Also, do NOT just try and stab any old compressor. Ever. The system is designed to run with one particular compressor. Start stabbing other stuff and you'll have big problems. Need the model number off the compressor to replace it with a proper one.
As for the brazing, that's standard. You're dealing with high pressures. Vehicles are done the way they are because they're made to be taken apart. Pulling motors n such would be difficult if they were brazed. Refrigerators and hvac systems etc aren't. They're designed to be put together and left to do their thing.