You would have to be an idiot to not think "Last Friday Night" would be the perfect late spring/early summer single. That song would smash, and then end the era. The album has a lot of single material, but it's too risky releasing 6+ singles.
You guys obviously do not know what's the point of choosing a single.
The record label doesn't give a **** about Hummingbird Heartbeat or NLTM because they are boring and aren't what is 'IN', 'NOW' or mainstream-type music that will be commercially-successful. They won't be commercially successful and will not be at the top of iTunes or even in the Top 10.
Katy's first 3 singles are mainstream songs that are appealing to everyone and are songs that people can sing along and dance to. They have a radio-friendly, mainstream sound that will be appealing to mainstream music listeners. ET is different and is less mainstream, but it has a hip-hop beat and mixed with Kanye West; could make the song hit the top 10.
After ET, I'd suggest 'Last Friday Night' or go to re-release singles such as 'Part Of Me' or 'Dressin' Up'. Part Of Me follows the same sound and production that Dr. Luke and Max Martin is known for and Dressin' Up is a throw-back to songs from OneOfTheBoys.
"Hummingbird Heartbeat" is a great song, but it is not single material. Radio would touch it because it's Katy, but it's only going to have the same success as maybe "Funhouse."