Union and per diem codes appear as soon as Costs is on

The Union Code and Per Diem Code fields show as soon as Costs is turned on, and you can create a code from the picker by typing it: the list offers to add the code you just typed.

Before this, both fields waited for codes to exist, and there is no screen for adding the first one. Adding a code that already exists now tells you so.

Cost codes, union codes and per diem codes are also available over the API and documented. Retiring a code means marking it inactive rather than deleting it, because time already booked to it refers to it by name.