Biking around the Easter Island (Rapa Nui) is a great idea. If you like to ride a bike, it is maybe the second best idea after the one you had when you decided to actually visit Easter Island.
I biked around the Island during winter, which seems to be a great season for biking if you are lucky enough not to see rain (I was lucky enough not to see rain at all during 5 days). I have not been to the Island in summer but I think it is probably not such a good idea to bike around the Island during summer (around 30°C and a lot of humidity).
In total, I biked around 120 km (75 mi) in 4 days. I was on the road (biking/walking/taking pictures) around 3-5 hours per day depending on the route I chose and the places I visited.