FaSSIF-V2 is usable for 48 hours from preparation.
For reasons of practicality and precision, we do not recommend making less than 250 mL of it.
Degassing the buffer is entirely optional. If you are using the media for dissolution testing, degassing can potentially affect how the dosage form disintegrates so you may wish to do so. However, we generally do not recommend it because degassed media reabsorb atmospheric gases rapidly and re-equilibrate quickly after degassing.