How to prohibit user from viewing a page before a specific time period?
<p>I want to build an online quiz test site. </p>

<p>Suppose, exam will start at 10:00 am and a student login to give exam at 9:45 am. Whenever the student clicks 'Take Exam' button, he/she cannot not get access to the question paper because the exam time is 10:00 am and there are still 15 minutes before the exam start.</p>

<p>Now I want to put some Javascript or PHP code that will prohibit the students to give exam earlier and if a students come early, it will show a stopwatch which display the remaining time before exam time and when the current time is equal to exam time then he/she will be directly redirected to the question paper page.</p>
