You had better take a meal in advance. Please understand that Himeji Castle is a cultural heritage: you will not be allowed to eat or drink in the donjon or in the special facility gEgret's Eye Viewh (gTenkuu no Shirasagih in Japanese).
I recommend that you expect at least 40 minutes on foot from a platform in Himeji Station to the facility, and 10 minutes more if you come via Shinkansen. This does not include the time for waiting in a queue.
Please exit passing through Central Ticket Gate. From the north entrance of Himeji Station, also buses are available, but you would soon find Himeji Castle even while walking. However, itfs a long way with steep slopes to get near the donjon.
I signed up on the website to reserve early.
So you have already read this page, right?
This website lists questions (http://www.himejijo-syuri.jp/guide/faq/) and answers in Japanese. According to the answersc.
: Visitors cannot eat or drink within the pay zone of Himeji Castle, which includes the special facility gEgret's Eye View.h
: There are coin lockers inside the castle near the entrance.
: The castle as a whole takes about one and a half to two hours. Visitation in the facility requires about 30 minutes.
: Reservation is not mandatory for admission to the facility but is recommended to make sure people watch exhibits and to ease congestion.
: In the special facility gEgret's Eye Viewh visitors should start from the waiting space on the ground level and go to halls on the 8th, the 7th and the ground levels in this order. In the hall on each level, visitors can watch exhibits freely, except in case a route is designated due to crowdedness.
: Major items, though not all, are given expressions in English.
: With the exception of flashlight shooting which is prohibited, itfs OK to take photos privately for non-profit use, as long as it does not annoy another visitor.
Actually also I am planning to visit Himeji Castle. My last-time visitation was made just before the restoration works began. I skipped then Nihinomaru of the castle and a neighboring garden Koko-en (pronounced with the first goh prolonged; http://www.city.himeji.lg.jp/koukoen/english.html). This time I hope to visit them and also stop by First Ri Connecting Corridor for shachihoko motifs (http://www.himejijo-syuri.jp/en/exhibition/#tower). So I now expect about 4 and a half hours in the castle and the garden, which may be extended.