We took the bus from Le Havre (2 euros) and spent one day in Étretat which was more than enough. We were able to climb the cliff and even lay on the beach for some time.
The walk you take can be as long as you want. If you like hiking, for what I’ve seen, you can hike the whole cliff. If you like the beach, you should know it is a rocky beach and the water is literally ice cold!
Oh, and for the people from Belgium: this is the perfect weekend getaway. It’s only 4 hours by car and you get an instant holiday feeling.