How long should one wait to shave their face after undergoing a facial hair transplant surgery?

Shaving the recipient area days after a hair transplant surgery may be an issue with your doctor.  If you really must shave, it really depends on how you have healed and it should be at the discretion of your doctor's recommendation. 

By your question, I am assuming you had hair grafts inserted into your beard area, and not removed from there via FUE. My advice to my patients is that after 10 days and for the first month they should avoid using a razor, since irritation and ingrown hairs may occur. During this time, they should use an electric shaver, as it is more gentle with the skin. They should also use a shaving cream designed for people with sensitive skin to soften the hairs before shaving and to help with the shave, and avoid after shave lotions that contain alcohol. A moisturizing after-shave lotion with aloe, however, is soothing and it will not hurt. But you should ask your surgeon about his routine, as it varies among different people. 

It
is important that you do not rush into shaving following your facial hair
transplant procedure. If you are still in the early stages of recovery, about
one or two weeks after the surgery, it is likely that you are still experiencing
scabbing. In order to avoid causing accidental harm to the region and
potentially delaying or damaging your results, please make sure to get the official
okay from your surgeon before shaving your facial hair.

This is definitely a question you should ask the doctor who did your hair transplant as different surgeons will give different advice.In general, it would make sense to wait until all crusts and scabs have fallen off and the transplanted area has completely healed before shaving.

You need to wait until all the scabs are gone and you have properly healed.  To be sure you need to do a follow up visit with your doctor and have him check and make sure you have healed properly.

I wouldn't rush, Wait at least one week after all of the crusts are off. The razor could catch the graft if it is not very sharp and pull them out. An electric razor would be better