The NI PXI-2548 does not require calibration because it does not have any electronic components that can get calibrated. Therefore, there is no calibration done, there are no ways to calibrate the module, and there is no calibration schedule.
Note that you can compensate for the insertion loss of the switch on a per path basis. These compensations typically include the loss through cables and are performed when the board is placed in the end system. This is more of an offset compensation for the system "switches+connectivity" rather than a board calibration; it is system dependent. I recommend making this compensation measurement before proceeding with any automated testing.