The First Few Weeks after Surgery

You should not consider, and probably won’t feel like, resuming sexual intercourse from 72 hours to a couple of weeks following surgery. Before you do resume sexual activity, remember that you will not be considered sterile for several weeks. Until your doctor determines that you are sterile, continue to use an alternate form of birth control.
And you should also remember that a vasectomy does not protect you or your partner from sexually transmitted diseases.

Once sexual activity is comfortable for you, it is important to resume ejaculation, since it takes between 10 and 20 ejaculations before any remaining sperm is released. In fact, sperm can remain in the semen for three to six months following your vasectomy.

You can expect your doctor to advise you when to bring in your first semen sample for examination. This is usually within four to six weeks after your vasectomy. You may be able to collect your seminal specimen at home and bring it directly to the doctor’s office or lab. Use the sterile containers that your doctor’s office will provide you for all semen samples.
Doing Your Part

Once seminal analysis begins, you doctor may advise you to ejaculate 10-12 times before collecting and submitting your first, and all subsequent, specimens to your doctor for microscopic laboratory analysis. You can expect to provide semen samples thereafter every few weeks or so.
You are generally considered sterile only after your doctor makes that determination.

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If he got snipped then he would have had all of this information before hand...