This could work
PHP Code:
public slowMo() {
for (new i = 1; i <= MaxClients; i++) {
if (!IsClientInGame(i))
continue;
SendConVarValue(i, FindConVar("host_timescale"), "0.5");
}
SetConVarInt(FindConVar("host_timescale"), "0.5");
}
Maybe run the SendConVarValue on a timer to make sure client dont change the value somehow