Is there a time limit in which shares sold short must be returned?

There is not a set time limit on the amount of time short shares can be borrowed. However, the shares that are sold short must remain available to borrow. If the shares become unavailable to borrow, the investor can be forced to buy the shares back in the market regardless of the current market price. This can happen at any time after the initial short sale has settled (2 business days after the short sale).