Yeah, there are 2 separate timers. One is visible. That is the de-valuation timer. For every house that is currently un-owned, this timer ticks down to 0 every 6 hours. At the end of the timer, the house gets a little cheaper and the timer starts up again. For a house that has been unowned for awhile(for instance, Louisouix on the euro data center has several hundred plots that have never been owned) it eventually hits a minimum price of about half what its starting price was.

That timer doesnt matter(aside from potentially saving a few gil). The invisible timer is the one that youre contending with. When a house becomes available the game assigns it a random timer that counts down server side. The consensus seems to be that the shortest of these timers are in the 4-6 hour range, and the longest are probly 24-26 hours(ive read no credible estimate for an "average"). Once this timer hits 0 anyone who meets the requirements(level, rank, and gil + permission if purchasing for FC) can buy the house either for their FC or for personal use. Before this timer hits 0 anyone who already has a house can decide to relocate to the empty plot. Relocation bypasses the RNG timer, but in return the relocators old plot is now available with a newly assigned RNG timer. Houses that havent been entered(the inside of the house, visiting the yard doesnt count) by their owner(or any FC member for FC housing) for 45 days(the servers are supposed to send warning emails to the account on file, but these are sometimes lost in the shuffle/junk mail folder) are demolished by the server(some lost furnishings can be reclaimed by the one who lost the house, but these expire after roughly a month) and become available for purchase after the same RNG timer. Any auto-demo's happen at the top of the hour, so someone scouting for newly opened lots is well advised to check the aetherytes at such a time. Beyond that, youre looking at luck and persistence(or buying an apartment for which there is a much higher limit... or playing on a less populated server). Personally, if i still needed a house i wouldnt even think about placard camping in the first 6 hours as its just going to frustrate and waste time(honestly, i might skip the first 12+ hours - lose out on a few houses but know that when i showed up to camp that the wait was at least halfway over). Take that last bit of advise with a grain of salt, as i do already have my house and have no desire to try and get one for an alt so im no longer involved in that part of the system.