楼主好!
单独来看（没有上下文语境）,这一句话基本正确：
We have more spare time than we did in high school.
【比较结构,可以用“代动词”代替这里应该用的have 的过去式had】
不过,变为
We have more spare time than we had in high school
表达更为准确清晰.
句子结构分析：
【 We主语】【 have 谓语】【more spare time宾语】【 than we had in high school 比较状语从句】
从句结构：
than 【we 】【had （the spare time承前省略相同的比较对象）】【in high school 状语】.
祝你开心如意!