There is no set schedule used by the Senate to decide when to vote on a certain issue, explains Vote Smart. A bill is typically voted on when the Senate Majority leader sets a vote, or when a budget appropriation for the issue has to be renewed or reallocated.
Legislation can be discussed in Congress without ever actually being called to a vote, which makes it virtually impossible to predict when the Senate votes on an issue. Unless a bill has an important funding deadline approaching or extremely widespread support, it is up to the Senate Majority leader to place it at the head of the agenda, says Vote Smart. A major Senate bill regarding immigration reform, S. 744, was brought to the floor in 2013 and experienced more than 500 amendment proposals before being called upon to put to a final vote, according to the American Immigration Council.