is it too late to book a demonstration time

As an extension from this, I went into the booking office today and there was no slots available from then on. I asked an office employee and she directed me to simply write my name in the slot I preferred with only two people maximum in each slot. I wanted to confirm this was accurate, is there allowed to be two different groups in one slot, and if not, what do I do because there isn't any slots available.

Also asking for the same thing, is it still possible to get a demo?