The most direct source of that information is your husband himself. Once an inmate reaches a work camp with a release date approaching, they typically know their out-date or have a very clear sense of the timeline. If he has not told you the specific date, asking him directly on the next call is the fastest way to get a concrete answer.
From your end on the outside, calling the facility and asking to speak with a counselor is the most reliable official channel. Counselors in work camp settings tend to be more accessible and more willing to share basic release information than staff at higher security facilities. A polite call explaining that you are trying to plan for your husband's release and asking whether a specific date is available is a reasonable request that often gets a helpful response.
The FI2 designation and the work camp placement are both positive indicators. A work camp assignment this close to a release date signals that the system has stepped him down through custody levels and is preparing him for reentry. That progression does not happen for inmates the system has concerns about, which means things are moving in the right direction.
The unspecified January 2018 date likely reflects the outer boundary of his release window rather than the actual date, and the fact that you were told he would be released prior to that date suggests the actual release could come weeks or even a month or more ahead of that marker.
Stay in close contact, keep the communication consistent through calls and letters, and have everything ready on your end for when that date becomes clear. Work camp to release can move quickly once the final pieces fall into place.