[Crayder]

This isn't something you would want to use a timer for anyways.

Make a variable that holds the last time the player executed. Example:

pawn Код:

PlayerInfo[playerid][pLastDropTime]

When the dropcar command is executed, do this:

pawn Код:

PlayerInfo[playerid][pLastDropTime] = gettime();

Before the command is executed you can do this to prevent use within 20 minutes:

pawn Код:

if((PlayerInfo[playerid][pLastDropTime] + (20 * 60 * 1000)) < gettime())
{
    // rest of command here
}

That's it! No timers needed!

Here is the full command:

pawn Код:

if(strcmp(cmd, "/dropcar", true) == 0)
    {
        if((PlayerInfo[playerid][pLastDropTime] + (20 * 60 * 1000)) < gettime())
        {
            //if(PlayerInfo[playerid][pJob] == 5)
            //{
                if(PlayerOnMission[playerid] > 0)
                {
                    SendClientMessage(playerid, COLOR_GREY, "   On a mission right now, can't use this command !");
                    return 1;
                }
                if((GetPlayerState(playerid)) == 3){//checks if passenger
                    SendClientMessage(playerid, COLOR_GREY, "   Hey, this isn't your vehicle!");                    // sends error
                    return 1;
                }
                GameTextForPlayer(playerid, "~w~Car Selling ~n~~r~Drop the car at the Crane", 5000, 1);
                CP[playerid] = 1;
                SetPlayerCheckpoint(playerid, 2506.9529,-2629.9968,13.6465,8.0);
                
                PlayerInfo[playerid][pLastDropTime] = gettime();
            //}
            //else
            //{
            //  SendClientMessage(playerid, COLOR_GREY, "   You are not a Car Jacker !");
            //}
        }
        else
        {
            format(string, sizeof(string), "You already sold a car, you'll have to wait %d minutes before you can sell another.", SecondsToMinutes(PlayerInfo[playerid][pLastDropTime]));
            SendClientMessage(playerid, COLOR_GREY, string);
            return 1;
        }
        return 1;
    }

ALSO: You should really switch to a command processor, using OnPlayerCommandText is stupid for plenty of reasons. I removed IsPlayerConnected in the command because that is useless, a player would have to be connected to execute a command. If you don't want it removed for some weird, stupid reason you should put it at the top of OnPlayerCommandText. You should ditch OnPlayerCommandText completely anyways like I said before. Use the best of what you got, command processors such as ZCMD, YCMD, iZCMD. OnPlayerCommandText is by far the worst option.