All lab check-off deadlines are at 11:59PM. (However, you need to get checked off by a TA or lab assistant, so you last chance to get checked off is during lab or office hours.)
To get checked off, you should prepare answers to the specific questions for each lab. You shouldn't feel compelled to memorize every single detail of lab. The goal here to make sure you're on track with CS10 and you should be comfortable with the higher level concepts for each question. For each lab the first questions are the biggest ideas, and the later questions are for your own benefit and review.
Remember: Even if you miss a check-off deadline, you can still get 50% credit for any lab check off at any time during the semester.