Two nights, with two full days (Tahiti flight leaves after midnight
)and we thought that was OK, not having any specialist must-dos. I'll disagree a bit with Denali here, as I think a (private) tour would be beneficial. If you take yourself, all you'll see are moai and they might all look much the same whereas in detail, they aren't. We did two single day tours, just three of us and driver/guide and it worked well. You could get away with one day and take yourself for the second or third days.
If you go in May, arrange your accommodation early ...
Easter Island bit from a
recent TR ... although if your miles are tight in the RTW, this will only exacerbate that 'problem' ?
Oh, in Peru and Chile look out for ceviche ... hope you'll love it. And pisco sours ... I've started making my own at home and they are a hit! (Having a lime tree covered in 'em helps)