legal ground
Article 628 of the Civil Code
The buyer shall pay the price at the agreed time. If there is no agreement or the agreement is unclear, and it cannot be determined according to the provisions of Article 510 of this Law, the buyer shall pay at the same time as receiving the subject matter or taking out the subject matter documents.
Article 675
The borrower shall repay the loan within the agreed time limit. If the term of the loan is not agreed or clearly agreed, and cannot be determined according to the provisions of Article 510 of this Law, the borrower may return it at any time; The lender may urge the borrower to return it within a reasonable period of time.