How can I set the first alert box to appear 5 seconds after the user has opened the webpage?

/***********************

MY PROGRAM

***********************/

document.write("Before you being, please open the console log in Google Chrome. Once you have the console log open, please click the console tab."
               + "You can begin now." + "<br>");


var question1 = prompt("Enter your name: "); 
var question2 = prompt("Enter your age: ");

function userDetails(name,age)
{
  /*NULL is represent a value that is not known*/
  /*Empty means that the variable is empty*/
  if(question1 === null || question1 =='')
  {
    throw new Error("The name field needs to be filled out. " + 
                    "JavaScript lets you create your own errors, which print directly " 
    + "to the JavaScript console, just like regular syntax errors do.");
  }
  else if (question1.length <= 2)
  {
    throw new Error("The name needs to be longer than 2 characters");
  }
  else
  {
    document.write("Name: " + name + "<br>");
    document.write("Age: " + age + "<br>");
  }
}

userDetails(question1, question2);

/*****************************************************************


******************************************************************/

document.write("Since we have your information, we can now play a quick game." + "<br>" + "<br>");

var question3 = prompt("Enter the number of days you work per week: ");

if(question3 <=7)
{
  document.write("Days per week working: " + question3 + "<br>")
}
else if(question3 >= 8)
{
  alert("INVALID! There are not " + question3 + " days in the week. ");

  var question3 = prompt("Enter the number of days you work per week: ");

  if(question3 <= 7)
  {
    document.write("Days per week working: " + question3 + "<br>");
  }
  else
  {
    throw new Error("Something went terribly wrong! There are only 7 days in a week.");
  }
}

/*****************************************************************


******************************************************************/

var question4 = prompt("Enter the number of hours you work per day: ");

document.write("Hours per day: " + question4 + "<br>");

/*****************************************************************


******************************************************************/

var weekly_total = (question3 * question4);
document.write("Hours per week: " + weekly_total + "<br>");

alert("Since we now have the number of hours that you work per week, you will be asked to choose a minimum number." + 
      "The number you choose will be used to generate a random number between the number of hours per week (Maximum Value) and your value (The Minimum Value).");

/*****************************************************************


******************************************************************/

var questionMin = parseInt(prompt("Please enter a minimum value please: "));

  if(questionMin >= weekly_total)
  {
    alert("This is not possible. The minimum value cannot be greater than: " + weekly_total);

    var questionMin = parseInt(prompt("Please enter a minimum value please: "));

    if(questionMin < weekly_total)
    {
     function randomGuess(min, max)
     {
      var randomNumber = Math.floor(Math.random() * (max-min + 1)) + min;

      document.write("Maximum Value: " + weekly_total + "<br>");
      document.write("Minimum Value: " + questionMin + "<br>");

      document.write("The random number is: " + randomNumber + "<br>");
      return randomNumber;
      } 
    }
    else
    {
      throw new Error("Booyah! Something went terribly wrong!");
    }
  }
    randomGuess(questionMin, weekly_total);