The treasury auction cycle constitutes weekly auctions in case of 3-month and 6-month bills and auction for every fourth week in case of yearly bills. These are for the treasury securities other than coupon securities. For coupon securities, there will be monthly auctions for 2-year and 5-year notes, and quarterly auctions for 10-year notes and 30-year bond.
On the pre-determined day, the treasury announces the amount of each issue to be auctioned. In addition to it, the auction date and the maturities to be issued are also announced. Occasionally, an outstanding issue is allowed to reopen (i.e., the amount of an outstanding note is increased at an auction instead of a new issue getting auctioned). In fact, the US Department of Treasury has reopened the 10-year treasury note several times in the past.