It's a day or so around the 10th as it's offset by maintenance as well. No one but Square knows the exact time for the release of the inactive plots. Since the timer was just suspended and not reset however, there are some plots that are getting demolished before the ones from the last land rush. I'd be a bit more vigilant about looking for a plot around the 10th-12th if you haven't found something before then, but just keep checking everytime you teleport into one of the major cities and hopefully you catch one listed (it'll show up as a white price tag instead of a red or blue name next to the plot number).