Ok, so I was told that it would take 24 hours to reach the boss
battle vs Kyogre in the Marine Cave, yet a day has passed and no
boss battle. Mods, someone, pls help out. Thanks :)
Seroiusly, it was annoying that I got the wrong info.
Here's proof
The mission can take a varying amount of time, from a few hours to
a few days. For whoever told you, it may have taken one day, but
for you it may take longer. This seems to be true for all maps