Good day, @l_ladams.
While there isn't an integrated calendar within QuickBooks Online, there are a handful of third-party applications offered that may serve the same purpose. Just head over to the official Intuit App Center and type Calendar in the search bar.
Please don't hesitate to reach out to me here should you need any additional assistance, I want to ensure your success. Thanks for dropping in, wishing you and your business continued success in all future endeavors.