Dr. Schmitt Patients

Hi there again.
After a patient has finished all the stuff they are responsible for, how far out
is
a surgery date? I have no idea how far out Dr. Schmitt is in surgery
appointments and I would love to give my employer (and my 500 clients) a
little heads up so that they can prepare for my absence.
Can anyone give me any info? What was your experience?
Any info would be appreciated!
Marlene