How about instead of chasing a wraith/kraken for 15 minutes without any reward and just delaying the inevitable for them to get to stage 3 and fighting at the power relay you encourages the delaying of the monsters feast. 20 minutes outside fighting is way to much for it to even have an impact on the game.
I made level 27 in the beta and not a single game has been close to end due to the time runs out. How about maybe lowering the time limit to 12-15minutes? And encourage the delaying so if the hunters played well the monster might have to force a fight when he is stage 2. Maybe also open up Power relay when its 2 minutes left or something like that preventing hunters from fleeing.
This is just a thought hope to get some feedbacks on the idea!
And thank you TRS for this non-planned BETA, never had such fun with a game!