Shigoto-osame means to carry out the last business of a year near the end of December, i.e. the end of the year.
It is stipulated in the law concerning holidays of government administration offices (December 13, 1988, Law No. 91) that the period between and including December 29 and January 3 is holidays for the Japanese government and municipal agencies, and that December 28 is designated as the last business day for the year or goyo-osame (another expression of shigoto-osame). When December 28 falls on Saturday or Sunday, goyo-osame will be December 26 or 27.
Many of the private enterprises follow this rule (with some designating December 29 as shigoto-osame), but financial institutions such as banks handle business at the windows until December 30. When December 30 falls on Saturday, financial institutions finish their handling of business at the windows on December 29.
In addition, January 4 is the day when business is resumed for the new year (shigoto-hajime, goyo-hajime) for government and government administration officies and financial institutions. When January 4 falls on Saturday or Sunday, goyo-hajime will be January 6 and 5 respectively. Some companies restart business on January 5 for the new year.