Your format will have had the advantage of inheriting the ISO8601 scheme for representing leap seconds (60 in the seconds component). With an epoch, you have to

Your format will have had the advantage of inheriting the ISO8601 scheme for representing leap seconds (60 in the seconds component). With an epoch, you have to either pretend leap seconds don't exist (typical on Unix), know when they all were before you can print a time or accept the drift (common with GPS units).