[M4D]

Please DON'T Use OnPlayerEnterVehicle In This case...
i'll Give you an example look at it and learn how i used timers, variables and SAMP functions from Wiki

https://sampwiki.blast.hk/wiki/OnPlayerStateChange
https://sampwiki.blast.hk/wiki/GetVehicleModel
https://sampwiki.blast.hk/wiki/SetVehicleHealth

Код:

#define YOUR_VEHICLE_MODEL X

new ExplodeTimer[MAX_PLAYERS];
new bool:IsPlayerInExplodeVehicle[MAX_PLAYERS];

public OnPlayerStateChange(playerid, newstate, oldstate)
{
    if(oldstate == PLAYER_STATE_ONFOOT && newstate == PLAYER_STATE_DRIVER)
    {
        new VehicleID = GetPlayerVehicleID(playerid);
		if(GetVehicleModel(VehicleID) == YOUR_VEHICLE_MODEL)
		{
			IsPlayerInExplodeVehicle[playerid] = true;
			ExplodeTimer[playerid] = SetTimerEx("ShowExplodeMessage", 20000, false, "i", playerid);
		}
    }
	if(oldstate == PLAYER_STATE_DRIVER && IsPlayerInExplodeVehicle[playerid] == true)
	{
		IsPlayerInExplodeVehicle[playerid] = false;
		KillTimer(ExplodeTimer[playerid]);
	}
    return 1;
}

forward ShowExplodeMessage(playerid);
public ShowExplodeMessage(playerid)
{
	if(IsPlayerInExplodeVehicle[playerid] == true)
	{
		SendClientMessage(playerid, -1, "Your Message Here");
		ExplodeTimer[playerid] = SetTimerEx("ExplodeVehicle", 5000, false, "i", playerid);
	}
	return 1;
}

forward ExplodeVehicle(playerid);
public ExplodeVehicle(playerid)
{
	if(IsPlayerInExplodeVehicle[playerid] == true)
	{
		new pVehicleID = GetPlayerVehicleID(playerid)
		SetVehicleHealth(pVehicleID, 0.0);
		IsPlayerInExplodeVehicle[playerid] = false;
	}
	return 1;
}

change X in this line: "#define YOUR_VEHICLE_MODEL X" to your vehicle model

good luck