IIRC, Badspot said to nest.
function serverCmdstopWatch(%client)
{
	if(!%client.isStopWatchOn)
	{
		%client.stopWatch = true;
		%client.timeStarted = getSimTime();
		
		messageClient(%client, '', "\c2Stop Watch started");
		
		return;
	}
	
	%client.stopWatch = false;
	
	messageClient(%client, '', "\c2Time: \c6" @ getTimeString(getSimTime() - %client.timeStarted / 1000));
}