Create the Proper Expectations
Students should be told to make sure that their internet connection is strong before they take online exams.
Consider allowing only half a minute (or one minute) per multiple choice question for non-calculation problems.
Turn Off Access to Review Questions
If the review questions are from the same question pools that the exam is being created from, make sure to close the review option when the exam starts. Otherwise, a student can open two windows (one for the exam and the other for the review) to check the answers.