Hi Eric,
Excellent question. We do all of our default QA testing using PHP7 and, while there are indeed known issues that we are working on in the plugin as a whole, none of them are PHP7-specific or would prevent you from using the plugin with PHP7 installed.
That said, we are big fans of testing everything in a safe staging environment when making any significant server or plugin update and would recommend you do so when updating PHP to ensure the calendar–among any other plugin, theme or component being used–responds well to it.
Cheers,
Geoff