From Halo: Reach, Reach fell on August 30, 2552.
However, the first Halo game occurred during May of 2552, as shown in the Private Jenkins cutscene. The time slot of the recording is 2552.5.27. May 27, 2552.
According to the canon, Reach fell after the Installation 04 was found, 3 months after.
...I'm really surprised about how bad of a slip up this is. It indeed seems as if an actual remake of Halo 1 is in order, considering the amount that was not said in it, including the fact that Reach fell after Installation 04 was found.
Unless of course, Reach was attacked, PoA jumped, Reach survived, and then was attacked again two months later. Which doesn't make sense given how surprised everyone is the Covenenant was on Reach during Halo: Reach.
Considering the novel/game relationship sucks in regards to consistency, I've kind of given up hope about the two canons working out. This however is an in-game inconsistency, and is pretty disappointing.
But I'll say again.
Reach Fell: August 30, 2552
Halo 04, Captain Keyes introduction to the flood: May 27, 2552
[Edited on 05.29.2011 8:21 PM PDT]