In the sentence, the phrase 'it's time' is used to refer to an activity that should have been done by now. It is used to refer to an activity completed in the past at a time in the present. The structure for such a sentence is:
It's time + subject + past verb
Thus, the answer must have the above structure.
Option A is incorrect. 'you has written' has a subject and a past verb but, the subject and the verb do not agree with each other. The auxiliary 'has' is used for third person singular pronouns whereas 'you' is a second person pronoun. Thus, it is a grammatically incorrect phrase.
Option B is incorrect. 'you are writing' does not comply with the required structure. The structure requires a past verb whereas option B contains a verb in the present continuous tense.
Option C is incorrect. 'for to write' is a grammatically incorrect phrase. It does not contain a noun or pronoun and thus, it does not introduce a subject in the sentence. Thus, without a subject a sentence becomes incorrect.
Option D is correct. 'you wrote' consists of a subject and a verb in the past tense. Thus, it complies with the required structure and so, it is the correct answer.