The wiki article for the ESB said that at the time, skyscrapers were 50% occupied by the time they opened and 90% occupied within 5 years. Now, there are two types. They either wait for a big tenant to take more than half of the space before starting construction, or they build “on-spec” and it varies but lots of them become 85-90% occupied within a couple years unless there are unique problems with that specific building