Upvote:3
The answer depends in part on your nationality. You can look up the default validity period at https://travel.state.gov/content/travel/en/us-visas/Visa-Reciprocity-and-Civil-Documents-by-Country.html/.
The consular officer may however issue the visa for a shorter period, but this is uncommon as far as I know.
Since the visa may be valid for up to 10 years (for some nationalities), and the fee for B and C visas is the same, you might consider applying for a B-2 visa instead.