What was the result? Given the drywall already had screws in place from a prior removal I'd have strongly suggested immediately opening the drywall and using a cup or bowl to scoop up the festooning bees and dumping them into a hive body with 3-4 frames removed from the center. Dump them into the space and very very quickly you'll have the queen in there and they'll be fanning the "here we are" scent to any airborne or other bees. They'll all settle into the hive body, you put in the missing frames, close it up and take it home. Giving them any time at all will allow them to build comb. A day or two won't hurt (and might have the queen reduced from flight-worthy to laying status) but you'll still have comb to remove (and probably just junk or crush/feed back to them).
Biggest worry is as D Semple and odfrank noted, homeowners often will lie or are mistaken about how long the bees have been there. If these are honest and friendly homeowners you might even leave the cavity empty, put the drywall back up, and keep the exterior bee entrance still open. Basically, a fixed swarm trap since that has caught swarms at least twice now. (homeowners willing of course, give them a jar or two of honey for each swarm they call you about).
I have had many a homeowner swear the bees "just moved in this last weekend". I'll go and find what is CLEARLY a huge massive hive that must have been there at least a year (and in my arid area of TX it really usually takes 3-5 years to get massive). So either the homeowner is completely unobservant and didn't notice all the bees for the past year, or what I find is when bees first move in the homeowners hope they'll leave on their own or die out like the media tells them happens for 30-50% of bee hives. My experience is that feral bees have a much higher survival rate though so the homeowner doesn't call until year 2 or 3. They may believe the bees from last year had died out and when seeing bees flying in the spring mistakenly think it must be a new swarm and must be small and attractive to the beeks.