Today at 8PM is the deadline that Major League Baseball teams have for adding players to the 40-man roster in order to protect them from the upcoming Rule 5 draft.
A quick primer on this is that players who were signed to minor league contracts (either drafted or signed as international free agents) who were under 19 when they signed, are eligible for the Rule 5 and have five years of professional play if not placed on the 40-man roster. Players who were 19 or older are eligible after they have four years of professional play and not placed on the 40-man roster.