Every single Halo game since Halo 3 (except Wars) has had at least one live action short.
Arms Race: July 10
Combat: August 28
Last One Standing: September 24
Halo 3: ODST
The Life: September 7
Deliver Hope: August 26
All three of these games came out in September. Due to Black Ops 2 coming out this year, I’m sure that 343i is going to want to avoid competition and release it in September/October.
Anyway the time from of these live action shorts are mostly in August-September. It can be assumed that August-September this year we’ll see a live action Halo 4 short.