Here's a schedule of the policy meetings that can move JGB and Nikkei futures as you mentioned.Although the Nikkie 225 futures both USD & Yen are excellent trading instruments just be aware that unexpected news from the BOJ has sent the index into very fast impulsive shocks from 400 to over 1,000 points. Does not happen all that often -just be aware of this.
http://www.boj.or.jp/en/mopo/mpmsche_minu/index.htm/