Planning on spening money a year from now doesn't stimulate anything for quite some time. But it does increase interest rates, at a time when lending is getting killed.
Buffet is a great investor and manager, but you can't map that ability to public policy magically.
Good point about the inappropriate delay in spending the stimulus. That said, if fiscal policy were pushing up interest rates the Federal Reserve could simply lower them and use monetary policy in place of extra fiscal policy.
This would present the risk of inflation, but if there were inflation (rather than deflation) we would not be in a liquidity trap requiring fiscal stimulus.
I think Krugman has gone over all of this. It's fairly well spelled out in Keynes as well.
Buffet is a great investor and manager, but you can't map that ability to public policy magically.