When I run a test configuration with several physical devices on the Robo Test Lab (from either the firebase console or by uploading the app to the play store), do the devices r
Devices are acquired and tests executed as quickly as possible, i.e. most of the time your tests will run in parallel on different devices at the same time.
There's no way to configure the tests to be serialized. You would need to do this yourself, by starting a test on one device and wait for it to complete before starting another one.