[feartonyb]

On top of script:

new ReportTime[MAX_PLAYERS];
forward ReportTimer(playerid);

Then make a public:

public ReportTimer(playerid)
{
ReportTime[playerid] = 0;
return 1;
}

Then add under /report command:

if(ReportTime[playerid] == 1) return SendClientMessage(playerid, -1, "You can use this command each 30 seconds!");
ReportTime[playerid] = 1;
SetTimerEx("ReportTimer", 30000, false, "i", playerid);