There are 3 x routes: 1 x Short, 1 x Medium, 1 x Long (to the peak of Diamond Hill). It is possible to reach the peak and back down in 2 hours if you have a good pace and only make brief stops. Please be realistic with your ability and speed, don't push yourself too hard and make sure to allow time to have a bite to eat.
Please make sure to keep an eye on the time - If you are not back within 2 hours, the driver will have to continue the tour without you, and you will have to arrange alternative transport back to Galway. There is a local / public service bus that passes near the national park.