Return the TimeInterval value between EpochUtil::epoch() and the current date/time. This is the default current-time callback implementation for current time retrieval. The obtained time is expressed as a time interval from 00:00 UTC, January 1, 1970. The resolution is: * Unix DG-Unix: microsecond resolution
* Linux: nanosecond resolution
* Solaris: 5 nanosecond resolution
* Windows 11: 1-5 millisecond resolution