Is the land already entitled? What kind of permits will you need? Depending on the complexity of the planning issues I’d recommend starting the planning process right now. Maybe the site’s ready to go, but if not there’s many issues that could potentially take years to work through with the City (Biology, soils, etc.) Besides, once you’ve got your entitlements, you typically have 2 years to start building, and even then you could get extensions. That way you could just sit back and wait to time the market to build.