But at the same time, there will be periods when I think is all that really hard work really worth my while?

句子中有二处错误。第一，句末的问号应改为句号。第二，is 应该位于hard work之后。

But at the same time, there will be periods when I think all that really hard work is really worth my while.

句子分析如下：

But at the same time 时间状语, there 形式主语 will be 谓语 periods 主语 （when 关系副词作时间状语 I 主语 think谓语 <that 省略> all that really hard work 主语 is 系词 really worth my while表语.)定语从句