The duration of the fill is a critical aspect of an approved run. If your run is 48 hours, then you media fill (simulation) must also be 48 hours at a minimum. Most companies will go even longer during media fills just to be sure. Otherwise an upset in your process can cause the batch to be discarded, or cause additional testing (done under an incident/exception/CAPA/deviation)
The volume/mass of the media isn’t required It is the number of units which is critical. You need to fill each unit so that there is enough to coat the walls of the vial, when swirled. But you have to leave enough air in the vials so as to provide oxygen needed to support microbial growth. So typically about 1/3 to 1/2 full is sufficient.
Don’t put an unqualified person in the area. Either qualify them and bring them in, or else rely on the cameras (if it is an executive/manager type person who just wants to watch) - most audits now require cameras so as to watch the process since access is limited.
Also, a media fill has a lot of details like the ones I’ve answered above. Make sure there is a definite goal/plan and description of your process, the interventions, your people, your filling speed, your duration, etc. Please feel free to ask additional questions online or through private message.