You have 5 days from the day of placing the new plot to the day your plot goes idoc and collapses.
a quick run down is as follows (copied and pasted over from the idoc thread stickied at top of this forum): -
Like New (unsure a couple of hours)
Slightly Worn - 1 day
Somewhat Worn - 1 day
Fairly Worn - 1 day
Greatly Worn - 1 day
In Danger of Collapsing 7-10 hours
Hope this helps