Dunkin' Brands Group Inc. said Tuesday its board has approved a $250 million share buyback program. In February, the company entered a $650 million accelerated share buyback program and received an initial delivery of about 8.5 million shares. Final settlement is expected to be completed by August. Shares were not yet active premarket, but have gained 19% in the last 12 months, while the S&P 500 has gained 14%.