This depends on the agent. Usually it's either 90 or 180 days.
Some agents, like Wegobuy, extended their storage period to 180 days due to Covid-19 backlogs.
After the time runs out your items will get destroyed.
If you're running out of time, there should be a simple way to buy an extension from the warehouse page. If your agent doesn't have that, you can contact the support.
added: 6/26/2023