For some reason after completing the Legendary Campaign of Reach I wasn’t awarded the “under 3 hour” achievement. In Career/Stats/Reach/Campaign , you can find a stat for Fastest Clear Time on Legendary and it’s there as 2hours 30mins 10seconds which is what I calculated my time to be as well. I hope they give me the nameplate, it was hard work. Has anyone else had this problem?
I am assuming you are using a secondary account to post here as I cannot view any level completions here on Waypoint for you.
Regardless, make sure every level has been completed, including the cutscene levels. There are 12 in total.
Had the same problem. I started “Epilogue” and the achievement procced for me. Had already ‘completed’ Epilogue on legendary, but it is likely the point the game checks for completion.