is it normal that, in-game, there is a slight delay between the visual effect of the hit and the actual decrease of shield/hull?
A. Weapon effects are purely cosmetic, the game doesn't actually care when a ship gets hit most of the time.
B. The game doesn't update hull/shield numbers on the infocard all the time to save resources. The game does properly do all calculations instantly under the hood however, so don't worry about the enemy ship living an extra second longer than it is supposed to.