Collage now offers an app for Slack that allows you to request, approve, and view time off directly from Slack. The Collage app for Slack can be activated via the Integrations panel in Company Settings:
For more information on using the Collage app for Slack, please see our support article here: https://support.collage.co/en/articles/7152355-setting-up-the-collage-app-for-slack