Isn't it about the time you ----- to do morning exercises?

虚拟语气
这难道不是你应该做家庭作业的时间吗?
根据分析,B 和C 应该都可以.
eg. It is about the time that you should finish your homework.
It is about the time that you finished your home work
it is about the time +did (should do)