The festival will be held from March 31 (fireworks on the evening of the 30th) to April 9. As I recall, from twelve years ago, the whole town is tinged pink by sunlight traveling through the leaves, and a veritable snow of blossom petals lines the roads.
I seem to recall the Navy base being open during the festival and, in fact, it is also a celebration of Admiral Yi Soon-shin.
Korean Tourism has some information and links to a report of the 2007 festival.
On other sites, I saw people advising against coming all the way from Seoul just for the festival, particularly as Yeoido has it’s own festival. Still, if you want the added value of possibly meeting the Surprises Aplenty family, you’ll come to Jinhae!