Only three weeks ago, On Prospect Park, the glassy Richard Meier creation overlooking Grand Army Plaza, was 60 percent sold according to The Wall Street Journal. Now Real Estate Weekly is reporting that the number has bumped up to 70 percent. And if you’re interested in landing one of the exhibitionist-friendly pads for yourself, best not tarry: Head of sales Cheryl Nielsen-Saaf expects the building to sell out within nine months.