As I understand it, banks do have to balance their books: liabilities, primarily deposits, must equal assets, primarily loans--by midnight of every day. Those created deposits--issuances of credit--are short-lived, as all loans are designated by the borrowers for some immediate purpose. The loans remain on the books while/until they are repaid. It is in that way that lending is constrained by the internal circumstances of banks: they must have sufficient liabilities, primarily deposits not created by a loan, on the books--with money held by the bank in less liquid forms, such as savings accounts and CDs, also counting as assets.