There is no set restriction upon how long one can hold a short position. You simply need to make sure you can continuously remain margin compliant and that the shares remain available to borrow. Note that shares which are borrowed are subject to recall at any time and if the lender recalls the shares and we are unable to locate replacement shares you will be subject to a forced buy in of your short position.
This is but one of several risks associated with short sales that you should be aware of (e.g., including potential unlimited losses should the share price increase, daily costs associated with hard-to-borrow shares, inability to exit positions due to trading halts, increased margin requirements).
Additional Information
- Overview of short stock buy-ins & close-outs in the IBKR Knowledge Base.