The Delivery Frequency is not closed. The paragraph you are reading should say that early clearance is not available in advance of you reporting ready. This is intended to reduce the workload for the Delivery controller as we will be changing runways when on 27 ops at 1500 local.
Requesting clearance from 1400L to about 1445L means the controller has to make a punt on your departure runway as that point, and then possibly have to change it when you do actually report ready.