Changing clocks and DST rules has a direct economic cost, entailing extra work to support remote meetings, computer applications and the like. For example, a 2007 North American rule change cost an estimated $500 million to $1 billion, and Utah State University economist William F. Shughart II has estimated the lost opportunity cost at around $1.7 billion USD. Although it has been argued that clock shifts correlate with decreased economic efficiency, and that in 2000 the daylight-saving effect implied an estimated one-day loss of $31 billion on US stock exchanges, the estimated numbers depend on the methodology. The results have been disputed, and the original authors have refuted the points raised by disputers.

What year did a change in DST policy cost North America somewhere between $500 million and $1 billion in extra work?