[Cameltoe]

My first suggestion :

pawn Код:

command(announcerestart, playerid, params[])
{
     new string[ 128 ];
     if(YOURGETADMINFUNCTIONHERE(playerid) < DESIREDADMINLEVEL) return SendClientMessage(playerid, 0x0, "You need to be at least DESIREDADMINLEVEL to use this command");
     format(string, sizeof(string), "Admin : %s [ %d ] has announced an restart, please park / land your vehicles.");
     SendClientMessageToAll(0x0, string);
     return SetTimer("OnGmxRestart", 30 * 1000, false); // Not sure if you could use SetTimerEx and call SendRconCommand("gmx");  inside it.
} // Zcmd

Then the function called by SetTimer,

pawn Код:

forward OnGmxRestart();
public OnGmxRestart()
{
     return SendRconCommand("gmx"); 
}