The main reason Zhang Yanhang was worried was that he might encounter some special circumstances along the way, such as being separated by only a wall from several dozen constantly moving Crimson Iron Ants. If that happened, Zhang Yanhang feared they might have fled by the time he arrived and would trigger his Death Wave Skill in response.
Consequently, that would increase Zhang Yanhang's Physical Strength consumption and correspondingly shorten his endurance time.
Nothing can ever be perfectly smooth sailing. That is why, considering the occurrence of some unexpected factors, Zhang Yanhang deliberately underestimated his endurance time; otherwise, even estimating it at seven hours would seem normal.
