This is the time line I've mostly, roughly, followed. (I may be off some, it's early and I'm tired.)
S1: Mar 2004 - California Primaries, an election year.
S2: Oct 2005 - During Palmer's first term.
S3: Oct 2008 - During the debates, an election year.
S4: June 2010 - During Keeler's presidency.
S5: Dec 2011 - During Logan's presidency.
S6: March 2013 - Said to be early in W. Palmer's first term.
Red: January 20, 2017 - Taylor's inaguration day.
S7: March 2017 - Set months after Taylor's inaguration.
Setting S1 in 2001 is, well, silly since it's an election year as established by the day's events. We'll just have to accept that 24's time has always been "off" with ours and the producers are on record saying 24 is an "perpetual now" meaning that "really" as the show goes on instead of it moving forward the events of the previous seasons just get pushed further into the past. So if it's "really" 2009 in 24's verse then Season 1 took place in 1996.