Folks, just wondering if there are any system variables or built-in such as current time etc .... I know you can use the action collection plugin but just wondering if there are hidden variables.

All Indigo Variables are visible in the Variable window.

That said, you can access all sorts of other internal data including current time, next sunset/sunrise time, Indigo Server version number, database name, etc., from the Indigo python scripting environment. So if you are wanting access from a script or plugin, then it is definitely available.