Place your bets, gentlemen. Casino developers have until 5 p.m. today to submit applications and a $400,000 non-refundable fee to the state gambling commission, in order to apply for a slot parlor license or development rights to a resort casino in greater Boston or Western Massachusetts. Six have applied for casino licenses, two are expected to apply for slot parlor licenses, and a Chicago billionaire is expected to apply for a casino or a slot license.