PA system setup is a big variable and comes down to quite a few points, the main one being how big your PA that you are using is?
This in turn is probably reflective of where you play your music and how many people are in your band or you may be a solo artist or DJ too.
I’d say from past experience of setting up small PA’s for a solo acts or duos, this also includes DJ’s, who are playing to a small venue with an amplifier, 2 x main speakers, microphone and maybe one monitor speaker would take half an hour to 45 minutes for the PA part of it etc not taking into account sound check and the ongoing tweaking of the graphic equalizer and levels for the instrument/instruments.
For a four piece band I’d say from past experience the PA setup should take around the 1 hour mark from start to finish.
Bigger than these and you may have the option of having roadies or you would be a little more experienced and know how long it takes to set your gear up I’d be thinking.
Remember this is only for the PA system setup, for full band setups you would add time to the above i.e. Setting up drums, setting up guitars and sound check etc.
I used to find most of the time was sucked up on load in and load out rather than the actual PA system setup, but with team work and everyone being aware of what their job is the time for setup would be minimal for the 4 piece size band, of course the drummer would finish setting up his set right at the end after everything was done, but I guess they have a little more hardware to setup.
Also for a while we were using mics place on amps or direct feeds in some cases and also mics on the drum kit or we would use a trigger and mic system and so these would add a fair amount of time to band setup and also in the end sound check.
So again in conclusion, “How long should a PA system setup take?”, how long is a piece of string?, it depends on the size of your PA system and how many people you have to help you, I’d give yourself plenty of time, coming from personal experience you just never know what is going to happen and what is not going to work on the night, I can remember soldering leads right up until start time on some gigs, the main thing is to enjoy every part of it and remember the prize at the end of the setup is that you are ready to play, so play well my friend.