Student or Learner
Teacher, is this sentence OK?
I will come in at 10 a.m., instead of 9 a.m., tomorrow and will work late today to make up my time.
Although it would be better, in my opinion, if "Tomorrow" were at the beginning of the sentence.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.