1991 Gulf War
The actual combat phase of the 1991 Gulf War lasted about 43 days.
Air war began: January 17, 1991 (Operation Desert Storm started) Ground war began: February 24, 1991 Ceasefire / fighting stopped: February 28, 1991
So there are two common ways to measure it:
Full active fighting period: January 17 to February 28, 1991 = 43 days
Ground combat only: February 24 to February 28, 1991 = about 100 hours / 4 days
2001 Afghanistan War
Start: October 7, 2001
Initial fighting end: Early December 2001 — Kandahar fell / the Taliban regime effectively collapsed, which is the more complete endpoint for the initial regime-toppling campaign.
About 2 month.
2003 Iraq war
Main invasion / conventional fighting phase, it began on March 20, 2003 and was largely completed by May 1, 2003, when the U.S. declared major combat over.
About 42 days.
All these actions are approved by US Congress so that US can use force for over 60 days.