CBO reports the time path of estimated outlays on government purchases under the proposed stimulus bill.
Assuming enactment in mid-February, CBO estimates that the bill would increase outlays by $93 billion during the remaining several months of fiscal year 2009, by $225 billion in fiscal year 2010 (which begins on October 1), by $159 billion in 2011, and by a total of $604 billion over the 2009-2019 period.
Is this too long a time frame to cause any benefit?
Yes, according to the tone of Greg Mankiw (maybe I'm reading too much into the "So"):
So only 8 percent of this spending occurs in budget year 2009, and only 41 percent occurs in first two years.No, according to Paul Krugman:
By my count, 70 percent of the Division A stuff and 91 percent of the Division B spending comes within the fiscal 2009-2011 window. If you go up to the end of calendar 2011, we’re probably up to about 77 and 96 percent. That’s not at all bad.