I know I can set a date for a coupon to expire, but how do I find out at what time it expires?

Presumably coupons all expire at some specific time on the selected date, eg. midnight (would that be midnight on the night before, or midnight after the specified date?).

I can't find any mention of this on the site.

I want to be able to offer a '48-hour special' and know that the coupon will automatically expire at the end of the 48 hours.