Each voiceover recording is limited to 10 minutes. This limitation is added to ensure that even in an unlikely scenario, if there is an interruption to the internet, you will not lose all the recordings at once. If you need to add voiceovers that are longer than 10 minutes to the project, please separate them into segments under 10 minutes. There is no limit to how many voiceover clips you can add to the project, but each voiceover can be at most 10 minutes.
Please see this article for more information about WeVideo's supported file formats and best practices for importing media to the project.