It looks like I'd have somewhere under 0.1 seconds to head for the phone or draw and start shooting. Since the scenario has me *knowing* in advance that these are criminals with guns, it appears to me that legality of using deadly force is not an issue.
I practice halfway regularly on spread-out multiple targets. When pushing myself to my limits, I can get at worst one hit on each of six targets with 8 or 9 shots. My "game" is to shoot each target once, and put repeats into one or two of them.
I can certainly be in tragic error, but it is my belief in my shooting that if I start first, and a group is bunched up, I own them.
What I do know is that if I worked in such a hazardous location, I would practice far more regularly, and more strenuously in each session. I would also give a lot of thought to the location of furniture, and any other security measures that might help *prior* to any need for action.
All that said: Were I a bad guy, I would case the joint, and possibly use some simple disguise and enter alone--thereby getting the drop on whoever's inside and making it easy for the rest of the group.