留空时间 meaning in Chinese

time at pickup altitudes

For civil purpose . the biggest advantage of the flying air boat is that it can anything that a plane can do but at the cost roughly of one tenth , the time of staying in the air is very long ranging from 24hr . - 72hr . ,
飞艇最大的优点是凡是飞机能做的事飞艇几乎全能做，但飞行成本比飞机便宜十几倍，留空时间长，一般飞艇空中飞行时间可达24小时- 72小时，以上这些均是大型飞艇。