Time was the enemy, and every passing minute counted as one minute closer to the day, hour, or minute when something happens, and he was powerless to stop it. Horrible things may happen to his friends, family, or those he swore to protect, and he will only be able to watch.
His only goal was to reverse the clock and push that minute back perpetually, so the day never comes until he dies and everyone he leaves behind can fend for themselves. When everyone he leaves behind is powerful enough to individually leave their mark on the cultivation world.
In light of this, Xasha couldn't afford to take days, weeks, or months to do something as fundamental as reinforcing his dantian when there were so many time-consuming steps ahead.