Hey Nic,
I think you should HOME your machine first, then while it is still HOME, ZERO the axis DRO's. (or, if you are using the G54 offset, select another offset, then zero).
Make the entries in the wizard .5" shy of the full length of the axis travel. Be careful with the Z direction !
The code will be in WORK coordinates, not machine coordinates but for this, they should be one in the same.
Russ