The weekend after Labor Day is traditionally the slowest weekend of the year at the box office, but this weekend could be an exception, given the unexpectedly solid results of last weekend, according to some analysts. Only one new film, Riddick, starring Vin Diesel, is opening wide, but a few box-office pundits are predicting that it could rake in more than $30 million. (Universal, which is distributing it, says it is looking for a much more modest $18-20 million.) Meanwhile, Lionsgate will be expanding the Spanish-language comedy Instructions Not Included to more than 700 theaters this weekend after it opened in just 348 last weekend with $10.4 million. In just those few theaters, it managed to place third on the box-office list during midweek screenings. Relatively strong performances are also expected for Lee Daniels' The Butler, We're the Millers, Planes, and One Direction: This Is Us.