Finally got to the Ursa Minor boss fight. Let me tell you how it plays out.
 
Tempest has an attack that she launches at the Ursa to lower its health. This attack recharges every two hours. Her attack has a base power of 12, but that power can be increased through “helpers”, other ponies assigned to help Tempest fight. In the tutorial stage, that pony was Bon Bon. On the second stage, those ponies are Wind Rider (250 gems, adds +8 to your power) and Nightmare Moon (1000 gems or $30 in the bundle, adds +20 power).
 
There are two rewards for each round. One is just for completing the fight, and the other is for completing it in a window of time. In this second round, you have 1 day and 11 hours (a total of 35 hours). With no helpers, it will require 13 attacks, and with attacks regenerating at 2 hours each, that means it can be completed in 26 hours. But that also means you have to check the game every two hours, or you lose precious time.
 
I’ll post another update once I reach the last stage.