We haven't been to Tunnel Gully for ages but the logging has finished (and put a new complexion on things). Two courses, one about 12km could take open women and vet men about an hour, riding level intermediate, navigation easy if you've done it before, but with a little maze section. And a shorter one 6km for those getting used to maps and/or bikes. Want a longer course? Put your hand up to plan one tee hee.
These are specified-order courses with interval starts, although we're completely fine with mates or families riding together. Ideal beginner adventure racing teams settling into communication on the move. If you're new plan to start soon after 10am, If you know what you're doing sleep in and start by 11am. The course closes at 1pm.
Take a look at the wellymtbo website for how we run MTBO events round here. The website has suffered the lack of a coordinator but will give you the general idea. You need a way to hold your map, we'll have some el cheapo mapholders for $5.