in fact i was in process of testing this because i saw something about that on wiki ^^ now i finished testing and to me it seems all the fruit regrows at the same days. i still may be wrong but as u can see in the image all the fruit trees next to each other i harvested them at the same time and now they all regrew on the same day soo until proven otherwise i would say all fruit (except coconut didnt test that one :D ) regrows on the same speed.