The Ship arrives above Gotham and linger for three full days, So the Batman family has three days of prep.

Imperial Dreadnought Specs
Length- 1,137 meters
Height- 690 meters
Weapons
2 Kree Disintegrator Cannons
24 Luphomoid twin energy blasters
10 Mobian energy harpoons
8 Xandarian Orienta-Type Air-to-surface missles
8 Deathfire bombs