Taxing flippers based on a graduated time scale is stupid. Speculators often do not want to rent out their stock because it's hard to get tenants out, so they leave them empty. The longer their stock stays empty, the more the problem of affordable housing is exacerbated. Why do they wait? Because they  want greater gains. Why give them a break in that case? Better to just tax speculators the same way, regardless of how long they kept their stock.