This depends on the size of the group, the hall, the equipment, and the expertise and preparedness of the live sound engineer and stage crew. Once all the equipment is loaded in and all the musicians are on site, initially checking each instrument could take very little time, maybe a few minutes for each instrument or channel. However, to get a good sound individually and as a group can take a lot longer, sometimes several hours or even the better part of a day. Dealing with poor room acoustics, or troubleshooting malfunctioning gear can take up a lot of extra time, so it’s wise to start as early as possible and leave enough time for solving those unexpected but inevitable problems.
There are times where a band doesn’t get to do a proper Sound Check, and the engineer will quickly make adjustments on the fly to mix for the room as the band begins their performance. This can be very challenging for musicians and the engineer, but it’s possible to get a workable sound in the hall relatively quickly, if the engineer is skilled. When adjusting the stage monitors, the musicians can help by signaling what they need to the engineer, as discreetly as possible.