Choose the option that correctly fills the gap: I wish I _______ more time to revise before the examination.

After the verb 'wish' expressing a desire contrary to present reality, the past subjunctive form is used. 'Had' is the correct past subjunctive here, indicating that the speaker does not currently have enough time. 'Have' would be used for factual statements, while 'will have' and 'would have' are incorrect in this subjunctive context.