it's your idea. I keep building all the time so far so if there was a connection between construction time and performance I would noticed that.
Also want to say that (I think I 've read all the posts of the forum
) I didn't see anything about this from older ones.
The only similar subject was about when the grass lv is update, the new grass can cause injuries in games or training.
Also that if you're playing with opponent that has low quality facilities (and grass), that can cause an injury in your players.
From my experience, those are "urban legends". Even if it affects, it's just a usual +- 1% which I believe none can have a solid conclusion from observing.