What is the shortest period a junior senator has served before becoming senior?

[Joe Republic]

Following the death of Daniel Inouye, Daniel Akaka is now the senior senator from Hawaii after serving for 22 years.  Of course, this comes just a few weeks before he leaves office himself, and is replaced by Mazie Hirono.

If Inouye's replacement is appointed prior to January 3rd, they will serve as junior senator until that date, and then immediately become the senior senator once Hirono replaces Akaka.

If, however, the appointment is delayed until after January 3rd, then Mazie Hirono will immediately become the senior senator upon entering office.

Has there ever been a circumstance of a junior senator serving even less time before becoming senior senator?  I can only think of Mark Udall, who was junior senator from Colorado between his swearing in and Ken Salazar's resignation just 17 days later.

[hawkeye59]

Lawrence Yates Sherman and J. Hamilton Lewis both became Senators from Illinois on March 26, 1913, with Lewis becoming senior senator due to the fact that Lewis is higher in the alphabet than Sherman (L is higher than S). So Lewis became senior senator immediately upon taking office.

[Starwatcher]

Elizabeth Warren will soon be the Senior Senator from Massachusetts too.

[Joe Republic]

Elizabeth Warren will soon be the Senior Senator from Massachusetts too.

True, I totally forgot about that.

[Lloyd Bentsen's Ghost]

Mark Udall became Colorado's senior senator pretty quickly after he was sworn in and Ken Salazar resigned to become Interior Secretary and was replaced by Michael Bennet.

[Joe Republic]

Yes, I mentioned that in the OP.

[Proud Lieberal from Northeast]

Ted Stevens served only 10 days as junior Senator. Mike Gravel was already Senator-elect, being elected in November 1968, but did not take his seat until January. In meantime, Bob Bartlett died and Stevens as appointed Senator in his place.

Almost exact mirror of Hawaii situation.

[Proud Lieberal from Northeast]

Lawrence Yates Sherman and J. Hamilton Lewis both became Senators from Illinois on March 26, 1913, with Lewis becoming senior senator due to the fact that Lewis is higher in the alphabet than Sherman (L is higher than S). So Lewis became senior senator immediately upon taking office.

Well, the same goes for Bartlett and Gruening, both of whom became first pair of Senators from newly-admitted Alaska (Bartlett ranking higher as former Delegate), as well as Oren Long and Hiram Fong, when Hawaii became a state (Fong ranking higher as former territotial Governor).

It's always a case with newly admitted states.