More like four-five months (August, 1990-Jan. 1991). And, Rumsfeld is said to believe we only need 100,000 troops, not the 1/2 million marshalled during Desert Shield.
So, if we started a buildup on the first of March, that would put us into June or July, so the timing is right.
Was he talking about 100,000 combat troops? If so, that means 300,000-500,000 in the theater, not counting the other 100,000 to 200,000 needed here for support. Also, allowances have to be made for the (unlikely) chance that other states will come to Iraq's aid, or that Iraq has deployable weapons of mass destruction.