Depends on what version you are coming from.
Also how many computers need to be upgraded.
If you are already on 6.3x, Probably about 1.5 hours main computer, 30 minutes for the others, which can be going simultaneously.
Main one takes longer because you may have SQL upgrade and you need to have it running so you know the others will have someplace to connect. You could run all simultaneously but if it fails at the main, going backwards is a major pain.
I agree with Wendell that if everything works, it should take about that long.
His point about successfully finishing on the MAIN first is particularly important.
We have had several upgrades go sideways and fail, which required a cycle of un-install, re-installs. For a plethora of reasons, we suggest the following:
<1> Full backup first, saved off the machine in question - seems obvious and yet ...
<2> If you are on 6.3.3 or earlier, you should have a minimum of a system restore point, if not a server image - there is no easy way back
<3> If you are a large/group practice and on 6.3.3 or earlier, expect that it will probably run slower, and know what your options are
<4> Leave yourself plenty of time - don't plan on fitting this in-between last patient and dinner
<5> If you use AC for billing documentation, know that there are undocumented changes, and at least have your billing current before upgrading
<6> Know your fall-back plan - what are you going to do if AC is closed for the night and your MAIN is now gobbered up?
<7> Use someone who knows AC, not an IT generalist - several folks have documented spending days and $1000s getting back up after a well intentioned generalist thought that this was a typical software upgrade and ended up spiking the MAIN.
