I'd expect very limited in store quantities. Reports suggest Apple will have just 3 million units available on November 3. Presumably most of those will go to some of the 90 million US customers. Numbers will rise to 48 million by Christmas so the in-store experience may be having a sample model to play with and then just putting your name down on the pre-order list and getting an email when a unit is available.
FWIW the X appears to have little practical difference going for it over the 8s for the $500 price difference (8 v X 64Gb).
I'm sorry for the delay. You'll be able to pre-order in store from today. The staff will be able to let you know the expected delivery time frame for your order.