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));
}