Time goes up by 30 minutes every afked turn, up to maximum time of 2 hours.
This is to prevent spamming attacks every 30 minutes while the other faction is afk, which is not what PW is about. It is supposed to be about battles and skill, and not about 24/7 activity and getting advantage while people in the other faction are sleeping.
Neither faction can stall the game completely, if they skip turns and the attack time goes up to 2h, they will keep wasting every attack and losing every defense, while the enemy faction can still instawin attacks as much as they want, just less often.
Even if the stalling faction eventually launches a surprise attack, they are already at a disadvantage because they already had lost several defence battles in order to get the timer up to 2h.