Is this a joke about how Americans don't properly wash their hands, or just the difference in how long the "Happy Birthday" song is?
...or that Iowa dedicated her song to the president?
The joke is the Marilyn Monroe version is much longer than the way most people generally sing it (due to her singing as over-the-top sultry as she did). I timed singing the normal version 3 times, and it does come out to about 40 seconds. The Marilyn Monroe version is about 30 seconds each run-through, according to the Wikipedia page's sound clip, or over 40 seconds if you include the introduction.
Even one is too long...!♪Hap~py Birth~day♬Mister Presideeeeent!To~ yo~u♪♬Hap~py Birth~day♪To~ yooo~u♬President...?Happy Birthday, three times! Got it!Hap~py Birth~dayThree rounds of this...!?(Skipped)
Everybody Happy~ Birthday~!!Countering noro.It seems that it's for the best if you wash your hands for 40 seconds. It seems you can estimate the time by singing the song Happy Birthday three times.