PlayStation Plus content will be added to the store through the month, and not just on the first publish of every month according to a tweet from the Official US PlayStation page. The tweet said that content will “continue to roll out all month, so stay tuned!” However, in Europe all the content will appear at the start of each month.
The US PlayStation Blog has added some weight to this. A comment from Susan Panico (Sr. Director of the PlayStation Network) says that “the content per month isn’t determined as day one content and is content that will be made available through the month.” But Ross McGrath on the EU PlayStation Blog said the list will “only change once a month.”