The Cache Time feature for the Google Sheets plugin is a different functionality specific to this data source, despite the confusing naming!
According to the docs:
The Google Sheets data source has a caching feature that makes it possible to cache the Spreadsheet API response. The cache key is a combination of spreadsheet ID and range. The default cache time is set to five minutes, but that can be changed by selecting another option from the Cache Time field. By setting cache time to 0s , the cache will be bypassed.
I do not see any panel options that would display the set cache time anywhere on the panel or panel legend. Perhaps setting the dashboard/panel refresh time to the same duration as the cache time could help ensure that the data displayed is as fresh as the last request?