public long getExecutionStartTime() {
			return m_executionStartTime;
		}
{@link net.grinder.engine.process.GrinderProcess} calls {@link #setExecutionStartTime} just before launching
threads, after which it is never called again.

@return Start of execution, in milliseconds since the Epoch.
ngrinder-runtime/src/main/java/net/grinder/engine/process/GrinderProcess.java