You will not have an extra two months.
The visa is valid once it is issued; even if you do not utilize (ie, travel) on the visa.
Unless canceled or revoked, a visa is valid until its expiration date.
Therefore, a valid U.S. visa in an expired passport is still valid. If
you have a valid visa in your expired passport, do not remove it from
your expired passport. You may use your valid visa in your expired
passport along with a new valid passport for travel and admission to
the United States.
A visa is a permit to enter the country. It is also not a guarantee of entry (you can still be denied by border control even if you hold a valid visa).
Generally on a B1 visa, once you enter the country - you are allowed to stay for 6 months (sometimes, up to a year on entry).
For example, you get a visa on July 1st valid for 6 months; you can travel anytime between July 1st and December 1st - after December 1st, your visa is no longer valid (even if you did not travel on it). It does not matter if you fly on July 2nd, or November 2nd - the visa expiry does not change.