Things stop when too far away

So I put a stack of iron in a furnace, walked away and swam around the ocean, and when I came back only 5 have smelted, I was gone for a while. I decided to test it, with timing how long it takes to cook 10 fish (1 minute 40 seconds) and then put 10 more fish in, walk away and come back after that amount of time, when I came back only 5 of them have smelted. This also happens with crops growing and animals ageing. To sum it up, when you go too far from things, they stop moving in time or stop preforming actions.