A typical quarter lasts around 30 minutes, including when the ball is out of play.
The 20km figure is not an average, but is on the high end of what the elite midfielders cover in a game. I don’t have an exact figure, but I remember watching a game where one of the players (Robert Harvey) wore a GPS unit, and the distance he covered was around 20km.
A centre half back would probably be closer to 10km though.
In terms of your question, I think it would depend on the position. For non midfielders, I think the running demands would be somewhat similar to soccer, but there are some major differences. The sprints in soccer tend to be pretty short, wherea’s in AFL a player might make a lead for well over 50m at 100% effort. Also if the ball goes to ground, you may have to follow up the sprint with another burst of energy to fight against the opposition for the ball .
Do you play or coach soccer? If so, what does a typical off season training setup look like?
Ever since I started playing Aussie rules I have been struggling to come up with a suitable training setup. The sport is a mix of speed and endurance, which are a bit contradictory, so it’s really hard to know how much to focus on each element.
edit - I realise that any Europeans or South Americans reading this might cringe at hearing their sport referred to as “soccer”, but it would be too confusing if I call it football.