We currently do not have the feature that lets you choose the length of the AI video clip generated on the platform.
Stay assured that we understand having this feature would be really helpful.
This has been a trending feature request from our user community, and is already on the product roadmap. We will be sure to update you as soon as this feature is live. :)
For further queries/questions, please reach out to our support team via the Help tab available on your home page.