From the HKDL calendar:
So it's a long time, and they are closing the whole attraction instead of just half of it just like during iasw construction. Hopefully they will add a stop at Mystic Point during this time.
Hong Kong Disneyland Railroad February 17, 2014 – early 2015 (service suspension
due to construction of the Iron Man Experience)
In other news, the Chinese name for Iron Man Experience has changed from "Iron Man's Headquarters" to the current "Iron Man's Flight".