I know this isn't what you want to hear, BUT, there is NO WAY, that I would go ahead with this plan. Every person reacts differently, and you've never had it before.
I have been having Botox for 10 years, and I have red pin prick marks afterwards, and visible lumps at every injection site. Sometimes, I also bruise. It is obvious for about 5 hours afterwards, and I hide away at home. My Botox Administrator is a Nurse and the best in the area, this is simply how my skin reacts.
In addition, you are advised to do facial exercises straight after Botox, to encourage the Botox into the muscles. So, things like frowning and scrunching up your face. You must also refrain from exertion (so walking around all day would be a no-no), and you must not lie down flat.
If you could have left the visitors at home, I would maybe go for it, as you could assess the situation afterwards and go home when you feel you look okay (and have maybe put on some concealer), but having to face them just minutes after treatment is waaay to risky. Unless you just tell them the truth, of course!