If he makes it to 7:19 PM, EST–so, three hours and a couple minutes–he breaks the record from when Strom Thurmond filibustered the Civil Rights Act of 1957.
Also worth noting, other Democratic senators taking turns to ask questions–very lengthy questions–to give Senator Booker a chance to rest his voice. These include Sen. Chris Murphy, Sen. Andy Kim of New Jersey, Sen. Peter Welch of Vermont, Sens. Dick Durbin and Tammy Duckworth of Illinois, Sen. Kirsten Gillibrand of New York, Sens. Tina Smith and Amy Klobuchar of Minnesota, Sen. Ron Wyden of Oregon, Sen. Raphael Warnock of Georgia, Sen. Chris Coons of Delaware, Sen. Mark Warner of Virginia, Sens. Elizabeth Warren and Ed Markey of Massachusetts, Sens. Chris Van Hollen and Angela Alsobrooks of Maryland, Sen. Maggie Hassan of New Hampshire and Sen. Ben Ray Luján of New Mexico.