My advice would be to test drive the HS prior to your order date, so you know whether its suitable for your requirements, it then gives you time to think about it and whether you want to test drive another car to compare it to. You are then not flustered on order date, about test driving and ordering on the same day.
The new HS is a cracking car, with some great offers across the range (petrol, hybrid+ and phev) nationally, which can be found in the Deals & Offers thread.