"To discourage the resale of plots, any plots relinquished by owners will be unavailable for purchase for a limited time.
* During this period, said plots will still be available for relocation."*
The exact nature of the timer has never been mentioned. Logically it follows there would be no reason to tell us if that exact nature changed at some point.
"A limited time" through observation seems to be 0-24 hours, supported by the fact that many houses sell out between 10 and 14 hours old, which is the top of the bell curve for a 24 hour period. If any plots are getting older than 24 hours, its fewer than one percent of one percent of all houses. And suspiciously the others are all statistically behaving as if they operate on a 24 hour timer.
*source link 4.2 patch notes
https://na.finalfantasyxiv.com/lodes...33e139e9792abf