Yea, that's on my end for writing a "spur of the moment" idea before putting more thought/consideration into it.
I'd say in-game years* (or roughly 5-10 in-game years), but idk how long that would take irl before you actually see your base/structures decayed or reclaimed by nature.
As far as how I envisioned "nature reclaiming player-built structures", I just figured that if you're going to abandon your base for a long time, you'd come back to a place that has tall grass, trees, or vines all over, not necessarily seeing the actual decay of the blocks, but just seeing that nature took over while you were gone, and now you need to mow your lawn.
absolutely!
just adding to the homo sapien experience of surviving through looming terrors like heat death and what have you.