Douyin does not provide the option to set up long-duration flash sales.

Douyin is a short video sharing platform where users can record, edit and share short videos, but there is no dedicated long-duration flash sales function.

If you want to share longer video content, you can try the following methods:

1. Record multiple short videos: Divide the long content you want to share into several sections, record and edit them one by one into independent short videos, and then post them on Douyin in a relatively coherent order.

2. With the help of other platforms: If your video content exceeds the time limit stipulated by Douyin, you can use other video sharing platforms or video editing software to publish and share your long video content, and then post relevant previews or clip links on Douyin.

Please note that the above suggestions are for reference only, and the specific operation methods may vary depending on personal needs and the policies of different platforms. It is recommended that you refer to the official website of Douyin or consult Douyin's customer support team for accurate help and guidance.