RoR 4中两个日期之间的差异不正确

Question

RoR 4.0.3 / Postgres 9.1.12

当我在PgAdmin

中执行以下查询时

SELECT extract('epoch' from expires_at) - extract('epoch' from now()) as secs_left 
FROM "auctions" ORDER BY "auctions"."id" ASC LIMIT 1

我得到expires_at（其类型为DATETIME）与当前时间（expires_at > now()为正数，否则为负数）的秒数正确值。
但是当我从rails执行查询时，我总是得到比正确值大得多的正值

@auction = Auction.select("extract('epoch' from expires_at) - extract('epoch' from now()) as secs_left").first
logger.debug @auction.secs_left

在控制台中我看到了

Auction Load (0.7ms)  SELECT *, extract('epoch' from expires_at) - extract('epoch' from now()) as secs_left FROM "auctions" ORDER BY "auctions"."id" ASC LIMIT 1
5472.91183400154

是什么原因？