解决方法
字符串格式的时间：
post.created_at.strftime("FORMAT STRING HERE")
# Without the influence of time-zone: I take it that you want UTC
post.created_at.utc.strftime("FORMAT STRING HERE")
链接strftime文档：
http://ruby-doc.org/core/classes/Time.html#method-i-strftime
获取小时,分和秒值：
post.created_at.hour post.created_at.min post.created_at.sec