On this page of the Tunic guide, you will learn how long it will take to complete the main storyline and how much time you have to spend "maxing out" the game to complete it 100%.
Length of the main story
The length of the main storyline in Tunic really depends on the ending you choose. If you are satisfied with Bad Ending, you can finish the game even in 7-8 hours. If you choose True Ending, which involves collecting all the pages of the Manual, the game time can take up to 10-12 hours, depending on your perceptiveness and focus.
It may take you at least a few more hours to complete the game in 100%. This is because you need to find 20 fairies hidden in all locations and also each treasure chest. Depending on your play style, it can take about 17 to 20 hours to explore every corner and complete the game 100%.