Thirty days

Hi,

If a date for re-payment of a debt is not set, the default halachic assumption is that the loan is for a thirty-day period. However, where local practice sets a different default period, this is the period that the lender and borrower should follow.

(Pitchei Choshen Halvaah 3:5, and footnote 12)

Have a great day,
Mordechai