I believe September 2nd is 45 days, so start looking then!

Mornings are typically best. I usually log on around 6am MDT, and as I recall, that's when I typically saw new empty plots that have sprung up. If you're gunning for a cottage, try to have 3,750,000 saved up, that way you have no limitations on the plots. You never know which one will pop and 3,750,000 is the most expensive. There's nothing more disheartening than seeing a plot pop up that you can't afford, so grind out that gil.