Official source is here to confirm your first three points:
http://www.12306.cn/mormhweb/zxdt/tlxw_tdbtz53.html
Originally Posted by Railway Ministry
自2013年1月1日起，互联网、电话订票预订第12天车票的起售时间由原来4个节点调整为10个节点，即 8：00～18:00（14:00除外）期间每小时均有部分新票起售，所有动车组列车（C、D、G字头车次 ）车票统一于11：00起售。具体起售时间详见各车站公告。自2013年1月4日起，互联网、电话订票预售 期延长至20天（含当日），预订第20天车票的起售时间仍为10个节点，代售点和车站部分售票窗口预售期延 长至18天（含当日）。
Quick and dirty translation:
Since 1 January 2013, internet and telephone presales opening times have changed from 12 days in advance at four times to ten times, every hour between 8:00 and 18:00 (excluding 14:00). Sales for all EMU trains (C, D, and G) are consolidated to 11:00. Specific sales opening times are listed by station below.
Since 4 January 2013, the internet and telephone presales period has been extended to 20 days in advance (including the day of the train) ten times a day. Presales at ticket windows have been extended to 18 days in advance (including the day of the train).
Can't comment on the last point regarding temporary cuts.