Legal analysis: If there is no repayment date on the IOU, the creditor can claim repayment at any time. The statute of limitations for IOUs without agreed repayment period is three years, and the longest statute of limitations for IOUs without agreed repayment period is 20 years. The limitation period of action shall be counted from the date when the creditor knows or should know that the right is damaged and the debtor knows it.

Legal basis: Article 188 of the Civil Law of People's Republic of China (PRC) stipulates that the statute of limitations for IOUs with repayment period is 3 years from the date when the repayment period expires. However, if there is no IOUs with repayment period, the parties can demand repayment at any time, and the three-year statute of limitations does not start to count, and the longest statute of limitations is 20 years.