A good few years ago, I used the stopwatch function on my (then) digital watch at a match at Maine Road.
The total "in play" time was 23 minutes in the first half, and just over 20 in the second. The match ended as a draw, with much timewasting by the opposition in the latter stages.
It's a lot worse today.
This topic comes up a lot, and I've always maintained that the full 90 minutes should be played. Footballers are supposedly professional athletes, and would soon realise that there would be no point timewasting as the clock would stop as soon as they started rolling around with a suspected double fracture of the cranium, only for it to miraculously heal itself when the stretcher party, doctor and priest arrive. As soon as the whistle blows, the clock and the match continue until there is no more time left, and the half/full time hooter sounds.
It happens in other professional sports, so why not football?