Actually there is not just one Federal Rail company in BiH, but two: ZRS (serving Republika Srpska) and ŽFBH (serving rest of the country), both "comply" with all European railways schedule calendar, thus major timetable change occurs on second weekend of December. However obviously on spot some minor changes might occur at different times, thus better to recheck via official websites of
ZRS &
ŽFBH or at the stations already in BiH
Also for links and some other info it might be helpful to check our Bosnia and Herzegovina page -
http://europetrainsguide.com/Countries/Bosnia-Herzegovina/Bosnia-Herzegovina-ZFBH/ZRS.html