warning: overflow in implicit constant conversion [-Woverflow] in Arduino Mega 2560 WI-Fi R3 - arduino

Question

i want to record a long data for like 2 to 3 hours using microcontroller Arduino Mega 2560 WI-FI R3 but I got this warning in my code
below is the picture of the warning i got.
enter image description here
the warning come up when I put the time out constant more than 30000 milliseconds
below is the code I used for the Arduino
#include "DHT.h"
// Pin Definitions
#define DHT_PIN_OUT A1
#define DHTTYPE DHT11
#define MQ3_PIN_OUT A2
#define MQ4_PIN_OUT A3
#define MQ7_PIN_OUT A4
// Global variables and defines
// object initialization
DHT dht(DHT_PIN_OUT, DHTTYPE);
// define vars for testing menu
const int timeout = 180000; //define timeout of 1 hour
char menuOption = 0;
long time0;
// Setup the essentials for your circuit to work. It runs first every time your circuit is powered with electricity.
void setup()
{
// Setup Serial which is useful for debugging
// Use the Serial Monitor to view printed messages
Serial.begin(9600);
while (!Serial) ; // wait for serial port to connect. Needed for native USB
Serial.println("start");
dht.begin();
menuOption = menu();
}
// Main logic of your circuit. It defines the interaction between the components you selected. After setup, it runs over and over again, in an eternal loop.
void loop(){
if(menuOption == '1') {
delay(500); //delay 0.5 second
// DHT11 Humidity and Temperature Sensor
// Reading humidity in %
float dhtHumidity = dht.readHumidity();
// Read temperature in Celsius, for Fahrenheit use .readTempF()
float dhtTempC = dht.readTemperature();
float Alcohol = analogRead(MQ3_PIN_OUT);
float Methane = analogRead(MQ4_PIN_OUT);
float CarbonMonoxide = analogRead(MQ7_PIN_OUT);
Serial.print(F("Humidity: ")); Serial.print(dhtHumidity); Serial.print(F("[%]\t"));
Serial.print(F("Temp: ")); Serial.print(dhtTempC); Serial.print(F("[C]\t"));
Serial.print(F("Alcohol: ")); Serial.print(Alcohol); Serial.print(F(" \t"));
Serial.print(F("Methane: ")); Serial.print(Methane); Serial.print(F(" \t"));
Serial.print(F("Carbon Monoxide: ")); Serial.println(CarbonMonoxide); Serial.println(F(" \t"));
}
if (millis() - time0 > timeout){
menuOption = menu();
}
}
// Menu function for selecting the components to be tested
// Follow serial monitor for instrcutions
char menu(){
Serial.println(F("\nSensor Array"));
Serial.println(F("Press (1) to start the sensor array"));
while (!Serial.available());
// Read data from serial monitor if received
while (Serial.available()){
char c = Serial.read();
if (isAlphaNumeric(c))
{
if(c == '1')
Serial.println(F("Now running the sensor array"));
else{
Serial.println(F("illegal input!"));
menuOption = menu();
return 0;
}
time0 = millis();
return c;
}
}
}
sorry for my bad programming and silly question, I'm new to this kind of thing. and I just found out that people usually get answers from StackOverflow, so I just wanted to try asking because I have tried to google the answer but I can't find it.