Slowing down time could reduce life expectancy, but Yu Liang had no room in his mind to worry about that at this moment.
If he missed this chance of the mall opening, he had no idea when the next opportunity to leave the rabbit-shaped deity's dream would come. That would be a real waste of life.
Moreover, since this ability could shorten lifespan, there should also be items in this supernatural world that could extend it. As long as he didn't overuse the mirror's ability, using it at critical moments shouldn't pose a big problem.
Now was definitely one such critical moment.
Yu Liang estimated the time, it was about seven hours till the time he had agreed with "it".
Seven hours later, daytime will come in the dream, meanwhile, in the real world, nightfall would come.
Yu Liang chose to slow down the dream's timeline by a factor of ten, transforming the seven hours into seventy hours. Meanwhile, he would lose about three days of lifespan.