Whats the validity period for a US B-1 visa for a Nigerian? [duplicate]

The confusion seems to be that there are two different time periods you could be asking about: the length of time the visa you are issued will be valid for and the length of time you'll be allowed to stay in the US when you enter with that visa. These are different numbers.

According to the State Department reciprocity page a B visa issued to a Nigerian will likely be multiple entry and valid for 2 years from the date the visa is issued. You can use the visa to enter the US as long as it is valid on the day you enter.

When you do enter the US the immigration officer you see will authorize you to stay in the US for a period of time that has nothing to do with the visa expiry date. From 8 CFR 214.2(b) a B visa holder may be admitted for up to 1 year, but in practice the admission will typically be for 6 months even if this extends beyond the expiry date of your visa. Note, however, that a 6 month admission is not guaranteed; the IO can limit a B-1 entry to time requested at his own discretion, and a B-2 admission can be similarly limited if the IO has good cause to do so and his supervisor agrees. You need to leave the US within the time period you are allowed on that entry unless you apply for an extension.

So the answer might be 2 years or 6 months depending on the question you are asking. The visa you are granted may be valid for 2 years but for any trip you take to the US your stay in the country will be limited to 6 months or less.