Computer training and handling cash and stuff should be handled afterwards iirc. But shifts-to-be will often start practicing running the floor, giving out directions, doing food counts, etc while still baristas, and a SS might try and explain things like the computer interfaces to the greenbean shift ahead of time so they know what to expect. This way they can get as much practice in as possible while there is definitely another SS there who can oversee and offer guidance. But the "official" training for post-promotion I think is limited to the computer training and cash handling.