Originally Posted by MathGuy42
found a new exploit that doesn't require clearing your cache. Details are here:
Basically, you take as long as you like until you get to the last save statue. Save your game there, then Exit Level (NOT Save & Exit). Then re-enter the mission from the map. You'll be near the end, but the timer is apparently reset to 0.
It worked for me and others who commented on the solution.
This is a great suggestion. I don't like doing the achievements offline if I can help it.
I'll give it a go for real, but this is the perfect backup plan if I can tell I'm going to cut it close.
Besides, doesn't sound as difficult as doing 'Speed Reader' in Halo:CE