How close to water do the tomatoes need to be to considered irrigated

It seems to be tied to ingame days: how many is unknown. It could even maybe a small chance every morning to spawn.

But if you were to get more Scaly Meat or get more statues from the super-strong monsters, sleeping over and over again should help spawning them instead of just waiting hours.

There's a sandbox island BUT you gotta sit through the whole story and quest part to get to it (you can access it early but don't have all the materials available).

Overall, I would say around 20-30 hours of story/quest before finishing the game.