It is what it is: pulpy, 1950s Heinleinian science fiction aimed at nerdy young boys.
The "four day planet" is Fenriss, a planet with a 2000 hour rotation rate. That is, any given spot on the planet is in darkness for 1000 hours, and sunlit for another 1000. Piper accurately describes the weather extremes that this would lead to: baking hot temperatures at noon, causing wild anabatic winds, followed by evening storms coming in off the ocean, followed by nighttime storms, followed by seriously below freezing temperatures at midnight, accompanied by wild katabatic winds until sunrise.
Against this background Piper tells the story of a pioneer colony, inhabiting the Four Day Planet so they can hunt "sea monsters" to obtain the long chain hydrocarbon molecules in their blubber.
The protagonist is a 17 year old boy reporter for a family-owned news service, investigating the corrupt government of the planet, especially as it relates to the monster-hunters, and the growing development of what a poli-sci professor would call an anarcho-syndicalist form of government when the monster-hunters rise up.
In between there are shootouts, and monster hunts, and intrigue, and forest fires, and blubber fires, and revolution and college applications.
Oh, and: there's not a single important female character in the entire book.