Jewish Year 5775: sunset October 3, 2014 to nightfall October 4, 2014
The holiest day of the year, the Day of Atonement (Yom Kippur), is traditionally observed with a 25-hour period of total fasting and intensive prayer and brings to completion the Days of Awe (the ten High Holy Days).
29 AND THIS SHALL BE A STATUTE FOR EVER UNTO YOU: THAT IN THE SEVENTH MONTH, ON THE TENTH DAY OF THE MONTH, YE SHALL AFFLICT YOUR SOULS, AND DO NO WORK AT ALL, WHETHER IT BE ONE OF YOUR OWN COUNTRY, OR A STRANGER THAT SOJOURNETH AMONG YOU: 30 FOR ON THAT DAY SHALL THE PRIEST MAKE AN ATONEMENT FOR YOU, TO CLEANSE YOU, THAT YE MAY BE CLEAN FROM ALL YOUR SINS BEFORE THE LORD.
If on Yom Teru’ah the books and gates are open, then atoning for sin between man and God occurs during the Days of Awe before judgement is sealed on Yom Kippur. (To atone for sins against another, one must seek reconciliation with that person, righting the wrongs committed against them if possible, all before Yom Kippur).
Source: Judaism 101