How many days to visit Easter Island, Chile

Most people visit Easter Island for 3-5 days. Personally I recommend 4 days/3 nights, which for me was the ideal amount of time to see everything I wanted to see on the island
Since it's quite far from everywhere else (it's a 5-6 hour flight or minimum or 7 nights on a cruise to get to it), it's worthwhile to stay on the island for longer to make the best use of your time
How to spend your time on the island:
The most famous attraction on the island, the giant Moai statues, are located inside the Rapa Nui National Park. The park itself will take 1 full day to explore, but ideally 2 days so not to rush it. The ticket to the park is quite expensive at, CLP$54000 (=USD$70), and is good for 10 days, so it's best to not rush it
Aside from the Moai statues, the island offers lots of other things to do, for example:
Volcanic craters: the entire island is formed millions of years ago from volcanic activities, and you can still see this geological history by climbing up to the top of volcanoes and look inside the craters, which are all lakes and marshes now. The two most popular ones are Rano Kau and Rano Raraku
Archaeological ruins: besides the Moai statues, there are other ruins you can see, the remains of various ancient villages around the island like Orongo, Ahu Akahanga, Ahu Vinapu, Ahu Te Pito Kura, Ahu Vaihu. These are spread around the island and it will take a good chunk of a day to see them all
Watch sunset and sunrise: there are great spots on the island to catch stunning sunrise and sunset views. The most common spots are Ahu Tongariki for sunrise and Ahu Tahai for sunset
Beaches: while Easter Island is not a tropical beach paradise, it does have two popular white-sand beaches of Anakena and Ovahe. Of the two, Anakea Beach is the bigger and more popular one, and Ovahe Beach is much more intimate
Star gaze: this was my favorite thing to do on the island aside from the looking at the ruins. It's so rare these days living in big urban areas to be able to see the sky as our ancient ancestors have, because of all the light pollution. Easter Island is one of the most remote places in the world and its night sky is very dark, making it an amazing place to get out and look at the stars and constellations. You can stargaze on your own within the town of Hanga Roa where all the hotels are located. The milky way is visible from here. But to get the best vieww, you need get away from the town and go north towards the Rapa Nui National Park. You can do this on your own too, but most people get on organized stargazing tour (the most famous one is Rapa Nui Stargazing, but many other tour operators also offer this)
Wander around the island: aside from visiting the various points of interest and ruins, it's great to just explore all over the island. The island isn't very big, just shaped like a right angle triangle that's 16km wide by 16 km tall, so you can easily get around the island by bicyle, ATM, taxi, or even horse. The island is mostly just nature, and ruins, and you will get to see some beautiful landscape
As I said before, there is no shortage of things to do on the island. You can spend 5 days there and do all the things I've listed above. But of course if you don't need to do everything. However at the minimum I would suggest spending at least 3 nights so you don't miss out on the top things to do