Swapping an Expansion Bay Module like an discrete GPU will take ~2-3 minutes:
1. Shut down
2. Slide out the input modules covering the Expansion Bay connector, and open the cover door.
3. Unscrew three or four captive fasteners to remove the Fan Cable or GPU Cable.
4. Unscrew two captive fasteners to release the Expansion Bay Module.
5. Slide out the Expansion Bay Module.
6. Reverse the steps with the new module.
It's not something we specifically designed to happen on the fly like swapping Expansion Cards or Input Modules, but it is quick enough that you don't have to plan ahead for it.