for twice as long as的使用方法

During that time the districts that stayed closed longest forced all or some of their children to learn remotely for twice as long as schools in Ireland.

这里for是什么成分？去掉可以嘛？

Indians are the world's biggest book worms, reading on average 10.7 hours a week, twice as long as Americans, according to a new survey.

这里为什么没for？

for twice as long as schools in Ireland为介词短语作to learn的时间状语。twice as long as Americans为形容词短语，作10.7 hours a week的非限制性定语。