Normally WebDriver should return control to your code only after the page has loaded completely.
So the following Selenium Java code might help you to find the time for a page load -
long start = System.currentTimeMillis();
driver.get("Some url");
long finish = System.currentTimeMillis();
long totalTime = finish - start;
System.out.println("Total Time for page load - "+totalTime);
If this does not work then you will have to wait until some element is displayed on the page -
long start = System.currentTimeMillis();
driver.get("Some url");
WebElement ele = driver.findElement(By.id("ID of some element on the page which will load"));
long finish = System.currentTimeMillis();
long totalTime = finish - start;
System.out.println("Total Time for page load - "+totalTime);