Upvote:3
It doesn't mention that because it's on a first come first served basis until all the tickets are gone according to Congressman's Posey's page:
Bureau of Engraving and Printing The Bureau is responsible for the printing and designing the nation’s currency, U.S. postal stamps, official invitations, and ID cards. During the tour, you'll see millions of dollars being printed. The tour features the various steps of currency production, beginning with large, blank sheets of paper, and ending with wallet-ready bills! Public Tour: 9:00 a.m. – 10:45 a.m. & 12:30 p.m.-2:00 p.m. (every 15 minutes). Extended Summer Hours (APRIL-AUG): 2:00 p.m. – 3:45 p.m. (every 15 minutes) & 5:00 p.m. – 7:00 p.m. (every 15 minutes). Ticket Booth: 8:00 a.m. until all tickets are gone. Visitor Center (Enter at 14th & C): 8:30 a.m. - 3:30 p.m. My office can attempt to schedule a tour for you if you contact my Washington, D.C. office at (202) 225-3671. Tour groups may not exceed 10 people.
Which you can schedule for the day you want rather then take a chance that tickets may or may not be available.