Jill,
The entire 'flowering season' of the serviceberries is very short-lived - you're looking at not much more than a week. Most of the A.x grandiflora selections are more 'pink' in the swelling/unopened state than most the other serviceberry species, but I've not knowingly seen Robin Hill, so maybe it is more noticeable; still gonna be pretty short-lived with regard to length of display.
Height to ~20 ft, spread ~15ft. Reputed to be more likely to assume a 'tree' like habit; most unnamed A.x grandiflora selections I've grown tend to be vigorous multi-stemmed shrubs; oldest are now 15 yrs old, and are approaching that 20x15 size.

If you're locked into Robin Hill, you're probably committed to paying a sizeable chunk for 5 of 'em; but, if you're OK with row-run apple serviceberry seedlings - which will be lovely, and great for the local wildlife, you can get 'em fairly inexpensively from a number of online vendors - small, but survivability is good, and they grow fast. Check out the offerings at OIKOS Tree Crops.