IT IS NOW UNLOCKED: I restarted the game and it popped during the loading.
Achievement not unlockingI hit the under three hours halo 3 legendary campaign ( check my service record, it’s like 2 hours and 56 minutes ), but the achievement won’t unlock.
On the MCC service record it shows me I have a best time for halo 3 campaign of 3 hours and 47 minutes, which I have not.
Anyway I’ll report a bug: in every game campaign menu, I can’t see any leardboards or speedrun time
Yes, sometimes the unlocking of achievements is delayed.
It actually happened the same for me for Halo 4. I did it in under 3 hours, but the achievement did not unlock until the next day, in which it popped up as soon as I opened the menu... and that was unexpected honestly, since I still have to start practicing Midnight.
This happened with many other achievements as well. They just unlock later on.
I can see my times on the campaigns menu, but not on some of the playlists. I have to directly go to the leaderboards in that case to see my own time.
For individual missions, you will need to hit certain times in order for them to show up. Not necessarily sub par time though. At least, that is what I observed in many missions across the games.